I read a study I think from Midwifery Today (?) which said that women who had an epi had 12% posterior rate and those who didn't had a 3% rate... so keeping active, no epi and leave those waters! One midwife said that the day she stopped rupturing membranes was the day she stopped seeing persistent posterior bubbies.

With back labour, some women find pressure helpful, TENS, water and also saline injections which midwives need to be trained to do. Hurts like heck apparently, like a wasp sting, but removes most or all of the pain. Lunges in labour are good to help move the pelvis hence the bub, as is walking and stairs.