Which side are you sleeping on? I always thought it was supposed to be the left side so that gravity could move the baby's spine to the left, but my midwife just told me that all her latest research says to sleep on your right side.
I also feel that although sometimes these things work ahead of time (hands and knees, birth ball, walking, posture, etc.), sometimes there isn't a whole lot you can do ahead of time. It's more important to keep doing these things during labor (esp early labor) and most posterior babies do turn before they are born.