Well...you speak of recoding classes. If you have only made changes to the plugin, I would try pulling the nokia syncml inheritance tree in and giving that a whirl. I don't really expect it to work, but it can't hurt to try.
So far as "how", if you're going to write code, pseudo code would be to
detect the "serial" port your bluetooth connection creates, open a com (or a cleartext socket, depending on your language) at 96008n1 on that port, then "print" AT+MSYNC to that com. I would like to think that once iSync starts getting the SyncML feedback that you could hand it off to iSync's SyncML interpreter and you'd be done.
A phone call to Apple support might clear things up a bit.
You'd hope anyway. :\