I didn't check it, but it might be possible.
If you check the _effect abilities in corespells, you can see that it's possible to call a spell at the start of combat, and when being hit. While I doubt using tags that aren't there will work (just because they usually don't), it's worth testing and worth checking. (Do note, however, that chances are very very slim)
I am not sure if this will work, but adding the <SpellTargetType>RandomEnemyUnit</SpellTargetType> makes it go for random unit. Try to add to your spell, and make 3 different game modifiers to shoot bolts. I am not entirely sure if it will cast on the same target 3 times or 3 random, but it's worth checking.
