If I'm going to bind movement and strafing to the left D-pad, (which is always "running" by default) I'm going to need a way to "walk" or "creep" without additional buttons.
Then it occurred to me. I could just have "walk" or "creep" or whatever be what happens when you move or strafe while crouching. You could crouch a little bit to "walk" and crouch farther down to "creep".
Crouching is a buttonless input using the head tracker, so there shouldn't be any technical problems.