Do you understand the current code? It really isn't very complicated. No physics is involved and there are not that many objects involved. It's mechanic overhead is very small.
If so, it's quite easy just to amend it slightly to create different object types.
I haven't tried to be clever here, but here is a very quick way of spawning different types. The code can be much improved, but this should give you some ideas.
Uses the very latest beta build r174.