Push Modifier Weight Node question

I tried painting weight maps on a Push Modifier Weight Node applied to a figure, but it appears that the push modifier is applied to the entire figure at once and you can only subtract from it. Is there a way to invert this; basically set the push to 1.00 but have all areas of the figure be *unpainted* and only paint weight (and thus height) where I want it?

Thanks in advance for any advice.