Two of my five babies were posterior and I had back labor with both.
Fortunately they were both homebirths so I was able to crawl around, sit on a ball, shower and get in the tub at will. My first back labor, #3 is my best labor and delivery as far as pain and relaxation, really everything. She turned right after mt water broke while sitting on a birth stool and was born anterior with compound presentation.
My other was #5 and it wasn't that bad I just had DH squeezing my hips together and pushing on my back with his head like these pictures. The first picture is during a contraction on the birth stool.
http://s184.photobucket.com/albums/x...backlabor1.jpghttp://s184.photobucket.com/albums/x...backlabor2.jpghttp://s184.photobucket.com/albums/x...backlabor3.jpg
Being on all 4s and having water poured over my back was great too.
http://s184.photobucket.com/albums/x...backlabor4.jpghttp://s184.photobucket.com/albums/x...backlabor5.jpg
I know that posterior babies and back labor can be very painful but it's not a for sure thing. I spent too much time worrying about it with #5. I saw the chiro regularly to first turn her vertex and then anterior. She did turn vertex but even with exercises and the Webster technique she stayed posterior until I was in the tub on hands and knees.
Both my babies turned less than 15 minutes before they were born and both labors were 6 hours with 10 minutes of pushing.
My posterior labors were not more painful, just different. However if I had been in a hospital on a bed I would have been miserable.
Good luck,
Keri