Answering my own question here:

It seems this idea is not original. And the answer is it cannot be done. It was tried in the development environment and trashed the desktop.

http://www.gossamer-threads.com/list...velopers/17035

Essentially the scripts that launch the desktop cannot tell the difference between users (i.e. they assume there will only ever be 1 user). One of the developers hacked away at it for some time and made it work, but has forgotten (precisely) what he did.

I take that to mean, it ain't gunna go as it is with a second user.