I suppose it's quite possible...
Never really thought about spinning a big airplane, but I'm sure it's possible. All you need is a stall in uncoordinated flight, and it'll happen.
The problem with multi-engine airplanes is when you're one engine inoperative...and a stall occurs. If under given conditions, a stall occurs before Vmca (i.e. the stall speed is greater than Vmca), the wings will stall before the aircraft uncontrollably rolls. (This assumes the flying pilot manipulates the controls in a proper manner and maintains coordinated flight.)
Conversely, if Vmca is greater than the stall speed (under the given set of conditons), the plane will roll before the wings stall.
In either of the two above situations, you'll not spin. It's when the two speeds are close to or equal...that's when you soil your panties. She rolls uncontrollably (you're in uncoordinated flight), and the wing (or wings) stall. Yep, you'll get a spin.
So, in Vmca demonstrations, you need to see what speed you'll stall at and then be careful about power/speed combinations to make sure she doesn't roll at or near that stall speed.
Many of the test pilots have the advantage of chutes to assist in stall/spin recovery. As we all know, during training and check rides, many unrecoverable spins inadvertantly occur. What a shame...
Tom