I just gonna answer my own question because I sort of figured out the answer. My installation is a wordpress single-signon.
There is no tricky binary code or similar, but it is a bit cumberstone to change from a standalone Q&A to a single signon. I think I only managed to do this because I have like 6-8 users on the site. I can probably be done in code for WP.
Basically, I had to:
1) Do a clean install
2) Align all userid, so they macth the ID in your WP. You have to do this for all tables with userid's in it. Basically if a user has done anything in Q&A you have to change the user's IDs to the one used in WP
3) Copy most of the data from the original standalone installation to the new one. I think I had to delete the options to make it work.