As in, rig up a speaker system so you can read out the charge list but he can't see where you are, and thus listens without having a target to aim at.

Full body-bind hex. Can't do diddly-squat if he can't move or speak.

'Course, if he's one of those annoying wordless casters, then you'll have to tranquilize him, not just paralyze him. Fortunately, there are drugs for that.

If it gets really desperate, I think the rules only stipulate that the Stu has to be alive when you charge him. They don't specify that he can't be bleeding from a major artery at the time.

~Neshomeh

Sneak up on him; open a portal underneath him, whatever. Just take him out of his continuum and into another where the laws of his continuum are not valid. Any place where Harry Potter has been established as fictional (Doctor Who, Buffy the Vampire Slayer) would do. In those worlds he would not be able to use his magic anymore.

On how he'll blast you into oblivion.

If physically, sneak up behind him and tranquilize. Restrain appropriately, and charge when he wakes.

If it's by some sort of magic... well, most continua have some sort of way of inhibiting their magic-users. Force inhibitors. Drugs. Stuff like that.

If he's developed a resistance to his native ones, either find the ones most similar to those from other continua, or find a group of friendlies (or an ex-Sue or Stu agent) who'll help you out. Highly unlikely that only one would be able to subdue him, though; Stu.

Er... um... write it out and send it to him anonymously? Then turn up the next day and blast him into oblivion from behind?

Yeah, I'm out of ideas now. ^_^;;

Is there any way to incapacitate him beforehand? If you can, find some way to render him unable to do said blasting before charging. Shooting out all four limbs (kneecaps and shoulders or elbows would be my bet) could do the trick, but I don't know the Stu in question. Other than that, maybe deceiving him, or simply use stealth. Remain undetected aside from voice until done charging, then just take him out from behind or in a blind spot.