Following on from a discussion I had with Grazie, I realised that Vegas doesn't have such a beast. Sure you can do it with a lot of fiddling around but an automatable FX that let you control the separation would sure be nice.
Come to think of it so would a proper stereo panner, yes, yes I know there's a pan pot in the track header but moving a sound source in the stereo field is not just about relative levels, it's about delay ( or phase if that's the domain you live in). And yes there are some very nifty tools for really futzing with the stereo image but they're not plugs.