I didn't know you could mod mods like that, but it makes sense when one thinks about it. On the other hand Forestry pitches an absolute fit (read crashes) if you remove its buildcraft API. On the gripping hand though IC2 seems to do just fine without it.
If you've never done it before, here's how I got it working (your mileage may vary). Backup your saves and make a copy of the IC2 jar (always good to work off a copy when you're likely to break things), open the IC2 jar and delete its META-INF, next in the ic2 folder delete the bcIntegration31x and bcIntegration22x folders, then test in a test world, and test in your saved game (you did backup your save just in case right?).
Also, I love a well organized file structure when doing things like this. <3 <3
In theory, should anyone trying this run into any problems as long as they're not running buildcraft?