FTDK,
A large number of "lighties" ask for B2 at CS, we don't even bat an eyelid at those requests. As 404 said, a number a ways to get them there.
I'm not sure what response you have got when asking (requiring backtrack?) at CS, however I could not imagine much more than a "confirm full length" query from the tower if you were after more than B2 (B5).
If you "require" 3196M in your lightie, you will get it, you will just have to wait in turn, just like all the A330, B737 and others have to when they "require" it.
CS runs a 3 min sequence (3 minutes between each arrival across the threshold average) during busy times, and sometimes it is less with sight and follows etc, so a 10 minute wait for backtrack is not uncommon for the jets, just plan for that in your schedule and we'll all be happy!