Just an idea:
See if you can have the enemy call an event on the barrel that causes the barrel to attach(I think that is what it is called) to his hand sockets, and then an event that unattaches the barrel at a certain point in the animation. You will also need to provide some impulse to the barrel in the preferred direction when it becomes unattached.
Of course, the hard part will be lining up all the animations, line the barrel up to the hands, make sure the barrel moves with the skeleton as it animates, etc.
Good luck!