Towing a RWD car backwards on a tow dolly is apparently not that rare, based on a quick internet search. Here's a nice thread on the subject:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25279904/srt/pa/pging/1/page/1.cfm

one of those enlightened discussions where the people saying you can do it are actually doing it, and the people saying you can't do it have never tried it. I know I've seen it often enough, including on the interstate.

It does look like there's two rules though - really lock the front wheels, and avoid a front end weight bias, e.g. sand bags in the trunk. For a long trip I'd be tempted to remove the rear flex disk and go forward.