Yeah you would have to write a special integration. Its pretty easy would be real easy if you had classifieds or reviewpost to see how they do it as all our products integrate up the line as in reviewpost you can integrate with the gallery. In classifieds you can integrate with reviewpost or the gallery. It would not take much to create one if you looked at the forum integration files. It would be as simple as changing the registration link and not all but most queries from $link to $db_link.
I am sure with the right time you can create your own if you tinker.