Sorry, I obviously misunderstood what you meant. Now I've read your first post again I understand what you mean. SOJO Web another WCE has made a tutorial on this subject using AJAX. It's a sticky at the top of the DataAssist forum but here's the link anyway showthread.php?t=9353
Apart from that I'm unable to help further but I'm sure others will chime in once the weekends over.
You might also try posting in the PHP / MySQL forum.