haven't read the thread, so sorry if you've already gone OP, or made a decision.
My experience - both my first and second DC were posterior. My 3rd DC was not, and the 3rd was by far the worst labour (because she was in an awkward 'chin up' position, though not posterior).
Labour 1 - DD was posterior until I was pushing. I used gas and air (didn't like at all) and then had some pethadine which I found helped quite a bit. The hardest thing was the constant back pain, even when there was no contraction - the pethadine helped with that, and helped me relax (whereas the gas made me very tense). She turned as I delivered her.
I laboured on my bath in a bath and birthed her on a bith stool - in hindsight not the best options for my pain, BUt she was born after 15 hours active labour and a 2 hour second stage (which is reasonable for a first labour I believe), and no epidural or other intervention.
Labour 2 - DS was not posterior for as long, and the labour was much shorter. I laboured on all fours, leaning over a bean bag, and he turned sooner I think (bit hazy). I only used pethadine, and found it helpful.
Labour 3 - Don't think DD2 was posterior (although she was in the days prior to labour, so maybe she was at the start of the labour too). But the labour was excruciating for other reasons.
So I wouldn't assume you'll need an epidural for a posterior baby. My tips would be to ask for pethadine/morphine early on and see if that kicks some of the back pain, and labour on all fours/leaning forward.
Good luck! :)