Get an innertube from a truck or car. Cut a band out of it approximatly 1" wide. Basically now you have a huge rubber band.
Loop it around the front part of both feet. Move your feet apart just to the point where the band starts to tighten. Now, keeping your heels in one place, "twist" your feet outwards tightening the band as much as you can. Repeat this 5 sets of 10 reps.