I managed to (with relative ease even!) implement the ability to change the shape of a sprite by using the collision masks generated by SGDK2. That's pretty cool. The physics engine has the ability to generate polygons based on bit masks. I was already 90% there -- just had to hook them together... align them. That's the tricky part. Still not sure if they're aligned quite right. I haven't uploaded an update yet, but hopefully I can work on it more this weekend and post another update soon.