Rebasing published branch

[Harry .]

My repository consists of 2 branches, a and b (actually bookmarks). 
Development mostly takes place on a, while b contains small changes to 
several files needed to produce a different type of build. I regularly 
rebase b onto a.


This is all fine and dandy, except that I have to force b to a 
lower phase before rebasing, then strip the old branch from the remote 
repository after pushing.


Is there a better workflow?