Can I prevent a bone from being moved by the playermodel sequences?

As an experiment of using the proportions method for extreme cases, I’ve put together a Claptrap playermodel.

http://vgy.me/83L5bY.png

Is there any way I can lock the pelvis bone, so that the wheel just stays locked to the model origin? Am I stupid, and should I just leave it rigged to an unparented bone?

Try this maybe?

Or this.