Oh, hes not expanding the portal, more like conjuring one and moving it, or conjuring one, expanding it a little bit, then closing it and redoing the process again and again. 

And if you want non lethal you should say. Because from what MC can tell, the aliens are going for lethal, and he can't do lengthy non-lethal ways of getting rid of them if his portals only stay open for a couple seconds at a time. And well, he has no problem going full lethal if they're going full lethal. And honestly every hero should do the same thing, I mean, if the joker keeps getting out and killing more people and they DON'T instantly give him the chair, well.... yeah.

I could pull that they're super powered arcane bolts or something... I dunno.