I know many of the sha256 based altcoins can be merge-mined along with Bitcoins and I'm far from an expert in cryptography but I think I have a basic understanding of how that works. I also know mining Bitcoins without special hardware isn't exactly profitable these days.. so I was wondering, is it possible to merge-mine any of the scrypt based altcoins?

For example, could I mine Litecoin and Feathercoin at the same time without having to run 2 instances of minerd or cgminer (or whatever other miner I choose)? If so I'd love to know how, and if not I'd be interested in knowing why it isn't possible and what (if anything) would need to be done to make those altcoins "compatible"?