How about occasional events in between dodging bombs (bomb-themed minigames, really)?
For example:
Have bunkers (one per player, minus one) placed around the map that can survive the bombs, anyone not in a bunker loses a life. Of course, there's only room for one in the bunkers, and one is destroyed every time a large bomb hits until there's one bunker and two players.
One player has a sticky bomb stuck to him and must pass it onto another before it explodes, done by coming close enough to another player. Experiment with various spells to make it interesting (for example, a speed-up ability or firebolt to stun other players. The current bomb holder is immune to stun, but every time he uses it, the fuse burns shorter by a certain amount).