I'll imagine you have looked through fetlife.com? If not, the poly and kinky
group regularly has queries about this and how to manage that (or to decide if you want to). I don't see anything in the last month or so really about the subject, but when people do ask, there are quite a few responders who juggle that themselves so it's also a good place to get more advice. Sparklepop seemed to have great advice from the D side, fetlife can net you a large variety of info from a sub's point of view too and other challenges people face with that dynamic.
There is also the Two Dominants
group, not sure that will be as helpful, doesn't look to be too busy but figured I may as well link to it.