This has been raised in the FSDT forum on more than one occasion and the answer is always that it is something they are working on. It still remains that you can only give the command to turn left or right on pushback. Obviously from 421 left is impossible and right means turning 180 degs in a confined area. You can edit the ini file if you want to allow a right turn push back, but it isn't really an authentic move.
One of my fellow members at BA Virtual said pushback worked OK for him at 421 albeit a rather curious path is taken, pushing out backwards on Victor first before reversing somewhat and ending up tail back towards 422. It seems I needed to get the latest AFCAD dated 6/3/2012, whihc now has improved things as he explained. It's a very weird pushback, but at least I end up facing the right direction, which is 99% of the solution