Another nice one.
Have you ever though of making your own higher powered in-line flash? Take a couple (2 or 3) of your 430's, straighten them out (in the pointed up / bounce flash configuration), then use a band clamp to clamp them to your lens hood. Basically, lay them parrellel along to the axis of the hood. Use some foam to protect your equipment and to prevent slippage. Your macro has a pretty good sized hood to be able to do this, and so does your 500mm if you want to get farther back.
If you do not want to go with the hill billy set up, you could try a Better Beamer on a camera mounted 580. They do not cost very much (about $40). I was thinking of trying this myself, and Joel has said that he has been using one. Basically it will focus your light to a tighter circle when you are back off your set up with the 500mm.
http://www.luminous-landscape.com/re...r_beamer.shtml
Pat