Just have him do a presence maneuver.  Presence is the skill that 'commands' and 'Leads'.

He creates an aspect like "Rally Call", "Boosted Morale", "inspirational Words". (against a fixed difficulty - depending on the situation  - or, if applicable, against an enemy's defense - like a Bosses Presence or intimidate)

He allows his allies to tag it and after the first tag, his allies have to spend FPs.

That said, there are ways to create extra tags:

A stunt:  When you create an aspect that boosts morale, your allies get an extra tag if one or more enemies has suffered a consequence/is fleeing/is Taken Out/Has conceded.

In other words, create a situation where, if met, they get an extra tag.

House Rule:  Lots of GM's award extra tags for success.  So, if he beats the difficulty by 3 shifts, award him an extra tag on the aspect.

Combine the effects:  a stunt that gives him a bonus to create an aspect + a stunt that gives extra tags + a house rule to give extra tags could lead to many tags.

Lots of great advice and suggestions!  Thanks again!

So, I have a player that keeps wanting to create AoE Stunts and I'm unsure if 1) I'm comfortable allowing them and 2) how they should be costed/structured if I do.

He wants to make a couple Stunts that let him:

1) Cause every bad guy in the area to be forced to attack him with their next action
2) Cause every bad guy who fails an Intimidation vs. Discipline roll to run away

Personally, I think both of those are too powerful as AoE effects.  Magic allows for zone-wide effects, but it costs an extra 2 shifts of power....which, in turn, causes the Wizard more stress or to make a less powerful effect and makes their control roll harder (possibly requiring a Fate point be spent to pull it off).
If I allowed these AoEs at all, I think I'd want them to cost a Fate point to use.

I've already let him take a stunt, from Fate Core, that will allow him to cause one person to spend their next attack against him.  And Intimidation can already be used to try to cow one person, possibly causing them to flee if they lose a Mental (or Social?) conflict.  But the AoE parts just make them really powerful.

General thoughts and advice would be appreciated.

Honestly, in my experience at least, the book is way off when it comes to its estimations of how long sessions take in-game, how long a scenario lasts, etc. The book seems to take it as a given that any one session is going to encompass several days of activity, while most of the games I've ran, a period of two or three days might take a dozen or more sessions, with each session picking up immediately where the last left off and the occasional timeskip of a handful of hours. According to the book, that would mean a character recovering from a bad concussion over the course of a couple hours instead of weeks, or Harry being able to use his force rings much more frequently than the canon suggests.

So while it may be a useful guideline, take it with a grain of salt.

My general guideline has been to have Significant milestones after mid-boss fights or some other equivalent accomplishment, Major milestones at the end of a Scenario.

Yeah, tonight is going to be my 7th session of my first Story/Scenario/Adventure and we've progressed just about 24 hours in game time.  There's been a fight with a Renfield and a bunch of Darkhounds, some investigations, some interrogations, and some character discussion and planning.  But I don't feel anything has progressed to the point where there should be a Significant Milestone.  I expect there will easily be another 5-10 sessions before they reach the end of this Scenario, depending on choices the PCs make, etc.

Your idea of giving out a Significant Milestone mid-Scenario, at a "mid-boss fight," and a Major at the end of a Scenario isn't bad.  But with an extra point of Refresh coming at the end of every storyline/adventure/scenario, I think the PCs will scale up in power too fast.  I do like the idea of a Major Milestone happening every 2-3 Stories/Scenarios or when a Big Bad in the world is taken out as I think that sets a decent pace.  I don't know, I think I'll keep with my progression.  I don't think Fate is as much about "levelling up" as some RPGs.  It's more about the stories and the characters' growth as people and as a group.  I've tried to give my players that expectation, so we'll see how that works out as we continue to move on.

I did start them out at Submerged, so it's not like they're lacking in power! 

Personally, I would not have potions or enchanted items be affected by a threshold at all. They're static magic bound into some inanimate object and inanimate objects can't be invited in. When their effects are used, no one is actively drawing on any magical power, as the magic is already set and self-contained.

So, when running Dresden Files, how often do you give out Significant Milestones?

The book suggests at the end of a Scenario (Adventure), but it also suggests this will happen every 2-3 sessions. I don't know about anyone else, but my Scenarios don't end that quickly. It seems to me that a Scenario is a specific arc that isn't finished until the bad guy's immediate plan is foiled or the immediate problem is solved.

But is that stretching these Significant Milestones out too far for the purposes of player advancement?  Thoughts?

Then again, the DFRPG already has that option built into it, if you know where to look.
Luckily, I do.
Harry and Billy talk about it in the sticky notes on page 200, where attacks are explained.

Oh right. Thanks for the reminder and page number about that!

yup.  it's an aspect.  it was invoked for effect and she was compelled to run.

Weapon 1 or 2 object shouldn't scare Mavra.   The important thing is WHAT it is...not what damage it can do.

Catch:  Your Story, p.185

Even the mere presence of the
thing that satisfies your Catch will cause
you discomfort (and may be grounds for
a compel or something similar).

Ah, good point. Okay, thanks!