I was trying to think of cheats that work if the pool just divided total pool income by shares submitted. My examples might not be the best... Most cheats don't harm the pool as a whole so much as does the steady 'set it and forget it' miners.

Back to the subject of dividing up the hash rate into smaller units though. I never looked at pool software but it seems like it's all about routing shares for miners to solve as they need them, plus accounting. If you could break the multiple coin mining jobs into single shares and and pass them out at random it would be fair and cheat proof. "If You Could". I'm guessing that there's an overhead to switching coins that makes that less efficient. Right?