Well, here's my thought, and hopefully it's easier than what you're trying to do:

As the troopers first run in, we simply see a couple shots in their direction and one maybe hits the wall next to them, sending up a big cloud of smoke, then we cut to the next scene. Seems pretty straightforward to me, no need to make it too complicated.

As for the battling afterwards, the idea is that the troops are now scattered and fleeing, and in their disorganized state the Ewoks take them out. Perhaps if we saw troopers in armor running away more (maybe we can find footage, but more likely we'd have to film it), it might get the idea across better, but that's why the battle continues. Perhaps it doesn't work, but it seems like a good idea to me. But hey, I'd rather have a good movie than be right, so if I'm the only one, please let me know, guys. I'd been hoping to get more feedback on the idea.