I'm going through this same crap right now. My baby is oblique. It's painful; the little bum was trying to flip into breech position and got stuck diagonally because he's a big kid. I went to SpinningBabies.com and have been trying what they say to do to get him head-down again. Also, sleep on the side where his head is... It supposedly helps. Also, I keep trying to lean to the side where his head is and bouncing on my birthing ball to try and get the rest of his body to kinda switch to that side so he can get unstuck. I figure it's worth a shot!
I have read in many places, though, that it's common for an oblique (or even transverse) baby to get pushed into a head-down position and become engaged during labor from the pressure of the contractions. Hopefully, if nothing else works, that happens for us!