When I first started in Martial Arts, I also pronated like hell, which screwed up my form. One thing that I figured out was to "grip" with my toes when I threw a punch or made a sword cut- anything which needed to be solid and perfect.
When you curl your toes, it corrects the pronation, it pulls your knees back over your toes (where it needs to be), and firms up your step.
Do you have access to some sand to walk on? Another thing that works is putting smallish objects in the floor and trying to pick them up with your toes (it's a great party trick, too).