am guessing if I shorted out the motor windings I would end up with a smoke grenade.
If we're talking about a 12v or 24v motor, with the inertia of MIG wire dragging a braked 15Kg spool - I don't think there would be a problem. Lots of wirefeed motor speed control circuits short the motor by turning on a second "driver" transistor ( e.g. a 2N3055 or a MOSFET ), and older Lincoln wirefeeders do just use NC relay contacts to stop the motor. When you release the trigger of a brushed cordless drill you'll see a spark at both brushes as the spinning armature gets braked to a stop.
( ....I wonder in these days of regen braking on electric vehicles if any power tool makers have thought of feeding the braking EMF back into the Li-ion battery ...? )