Well, in the cannon they are tied to the personality of the warden that used them. WOJ says that someone "could use another warden's sword if he became enough like them. Morgan's sword for example (smirk). If he shared the same kind of psychological profile as Morgan, if he ever got beat into that shape, he could probably be able to pick up his sword and use it. " So by that it could be problematic to hand out used warden swords to your minions. But what if in killing the warden, Justin used some crazy necromancy similar to corpsetaker's and trapped some barely sane portion of the former Warden's soul in them, as a mechanism to activate the power. So instead of doing it however the normal wardens do, they have to mildly dominate the spirit of the blade, or some such, but can also channel a certain amount of the former wizards magic, like how harry ate the Kravos ghost and got one of his spells briefly.
Just a thought.