Add a switch to stop Rotobrush from propagating

I like to set some ‘key frames’ where I use Rotobrush to tell it how I would like it to mask. E.g the first and the last frame of a clip. But unfortunately, when brushing the first frame and then jump to the last frame to brush that, the tool starts propagating already, using a lot of resources and kind of freezes. I would like to see a button to manually stop and start propagating, when needed.