Nope. They said they weren't putting in any sort of brush option for freehand drawing and keeping it to parts from the game to preserve the art style. The only way to "draw" is to get very creative with existing parts and shrink/texture/color/layer/rotate them.

It's very tedious, and has kept me from doing a lot of things because there's no simple way to just make a curved line or stretch an object only along one axis instead of as a whole.