It's really easy. Just replace the original xfire_games.ini with this one and have Xfire 'Detect Games'.
You can also edit the xfire_games.ini yourself, if you already have an edited xfire_games.ini. Search (Crtl+F) for Freelancer in the file (open it with Notepad). Then add the following line above the ServerStatusType=FL
DetectExe=*\Freelancer.EXE
Save the file.
Have Xfire 'Detect Games'.
Enjoy.
Grtz,
Gust
PS: If you find anything that's bothering you with this, share and someone (maybe me, but I doubt it =P) can think of a solution for it, because this isn't perfect.
For instance, it would've been better if the launcher wasn't recognized as the game, but it's not really a bother though. I don't know how to solve it anyway.