Creating a paintbrush tool?

Does anybody know of a way to replicate a paintbrush tool in Matlab? Something similar to the way that imfreehand() in combination with createMask() can be used to create a mask? I have tried the following code with button down/move/up:

XY = get(gca,'CurrentPoint');
circleBrush = imellipse(gca,[XY(1) XY(3) SIZE SIZE]); % size is the size of the brush
mask = circleBrush.createMask();

However, it is very slow as it generates a mask every time the mouse is moved. The end goal is just something that can be 'burned' into the original image to make it all zeros. Anything is helpful and appreciated. Cheers