Evocation is pretty powerful and doing multiple tasks is more the realm of thaumaturgy or evothaum. With that said, there's a few ways to go about it.
First: overflow
(YS214)
If the attack succeeds by over 3 shifts, you could put the shifts towards something like a maneuver. The overflow rules are pretty adamant about having those extra shifts go towards something non-combat related. Like a supplemental move. I might allow for a scene aspect but probably not a targeted aspect. It really depends on how lenient you want to be as a GM
Second: Invoke for effect
Instead of doing damage, you do a powerful maneuver. As a GM, I tend to look at the power of the maneuver and the amount of shifts that someone fails to defend and decide what happens.
I use the breaking/lifting chart as a guide for maneuvers.
Example: If you hit someone with a power 8 'Wind-swept' maneuver, you invoke for effect.
Invoke for effect is, basically, a compel. So what's a fair compel? How badly did they fail? Is the maneuver sticky or fragile?
Then, I look at the power of the spell: 8. The right kind of power 8 spell can, basically, smash through a brick wall or lift a car. Hitting someone with that kind of power will probably do damage. So I might say, he gets thrown back a zone or two and takes stress. The stress and movement were all part of the compel.
If it was a mook, I'd say that a power 8 maneuver might take him out. He gets blown out the window and is lying unconscious on the street (he concedes). I think that's fair because a weapon 8 attack would have killed him anyways.
(this is my preferred method)
Third: A stunt
I haven't really delved into this. But it seems reasonable, that if you spend refresh on it, you could do something. I would somehow restrict how many shifts get allocated to a specific task.
Also, you should consider, do they have to make two dodge rolls? one for the maneuver and one for the damage? to dodge a maneuver, you dodge the Power of the spell. To dodge an attack, you dodge the targeting roll.
So what happens if, on their dodge roll, they fail to dodge the targeting roll but succeed in avoiding the maneuver?
It's something you'd have to work out. I don't know the best way of doing it.
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Doing damage and blocks seems unfair, IMO. As soon as you throw up a block against movement, you can no longer take supplemental moves because now they need to do a sprint action to move.(which totally F@#ks Characters with speed powers). So it's always advantageous to throw up a 1 or 2 shift block along-side your weapon attack.
Or, if you have a low athletics, put up a 4-shift block along-side your weapon 2 attack. Boost your discipline/control super high so that they take piles of stress from the targeting roll. Now you're hitting them for 2=stress+shifts AND you're always dodging their attacks at 4 shifts. Ugh. And that's only a 6-shift spell. You can easily pull that off at Chest Deep.
There's my 2 cents.
Edit: Another way is I'd allow you to hit someone with an ice attack, then spend a FP to say they are "frozen in place'. I reward the target with said FP.