I don't need to lock on to strafe. I use a controller on the PC version on occasion, and left\right on the stick functions just like a strafe. In order to change the direction my character moves in, I must use the right stick to change the camera angle.

I don't remember the exact settings I have, but mess with the legacy controls. The functionality you are looking for is there. You will need to combine it with the right stick to circle strafe if you don't want to lock on, but the functionality is definitely there.