[_ck_]

It’s a good question and something I vaguely remember reading before around here.

In theory (don’t try it until you hear from others) you could rename the bbpress user + usermeta tables for wp, and then tell bbpress to look at the wp tables like a typical integration.

You’ll also need to install several plugins and tweaks to make sure that wp registrations are properly handled on the bbpress side.

(whatever you do, backup first!)