Yes I mean two separate physical servers from two separate web hosting companies. I think there could be a way without compromising security, by simply populating the phpBB registration for fields, so that the user it still required to confirm phpBB registration at that point. i.e. they would still need to enter the captcha confirmation code.
Not sure how to do this, however I don't think this approach would compromise security. It effectively would be a semi automated approach and the user could opt out if they did not want to join the forum. I’m not really a php / MySQL programmer, but conceptually I think this could be done without too much effort by an experienced programmer.
bkeaton, regarding your "Yes" answer, what would you suggest as an approach to this could be ? I gather there might be several approaches to this, ranging in complexity, performance and security.