wasn't working when I tried it.
Found a 100% evil and annoying to maintain option though... stick Buildcraft into the .jar and then leave any sub-mods in the mods folder.
Not sure if this'd work for anyone having the same problems with IC2 as i'm not sure if it likes living outside it's jar in the mods folder or not.
It should, because MLMP should load the mods in the minecraft(_server).jar, then move to external ones. And IC2 works just fine outside it's .jar. You _could_ extract the files, throw them in a .zip, and name it something crazy, and it'd still work just fine.