Shoot the controller with lightning reflex?
Might accidentally trigger it, if the guy isn't bluffing, then that would bad. But if that goes well, then we'd be all happy and dude might lose his hand in the process.
That or just snatching the controller, because then we could take the guy captive and interrogate him later.
Or shooting him, but he might press it just as you shoot him or something. That or if his finger's right on it, shooting it might cause him to press it somehow after he dies.
Or we can do sort of a combination of the two: Have one of the squadmembers shoot him while Dex grabs the controller.