My only suggestion really, is to try what I wrote above. Hopefully the second machine will correctly pick up the playlists from the now-shared library structure/files.

Apart from that, I think you'd have to use something a little more sophisticated, such as another program or script to propagate a playlist from one iTunes DB to another on the alternate machine or a network share.

All solutions will invariably be hacks, since iTunes wasn't designed as a client/server system.