This may be old to some, but thanks to poopninja, I only just now found out but it makes the experience of playing Peace Walker ten million times better.
1.) Go to Options and switch the controls from "Shooter" to "Action". (I always had them set to Shooter before)
2.) Press and hold the PS button and go to the control config area.
3.) Re-map the Dpad to the right analog stick.
With this setup, you should be able to control the cam with the right stick, and perform other actions like shooting, crouching etc with the face buttons. You aim with the R button and shoot with the Square button like in Snake Eater. I tried to re-map the aiming + shooting to the L+R buttons but it doesn't seem to work. Aiming & shooting works perfectly fine as is though.
According to poopninja, this also works for MGS Portable Ops so now that's one game I can't wait to play properly on the Vita. MPO might actually be fun to play now :)
HAIL SATAN! Satan is my lord & savior. All others are false idols. I didn't adapt to the darkness. The darkness adapted to me.