Just came across this thread as I have been trying to do the same thing
we are on 6.0 U1a vCenter and have Prouction on 6.0u1a (plus CBT fix)
however all our dev is on holder hardware on 5.0 and I want to move this to 5.5 (6.0 is not supported int he HCL)
are we saying I have to do this manually?! I don't know what to say to that!