I do this all the time. You don't need anything that complicated. Apply a levels or color correct to the layer, and then start your rotobrush. Rotobrush will "see" that the color correction is in front of it in the effects stack. Do all your roto work. Then "freeze" the rotobrush. Then you can turn off the effects and it won't affect your roto work. Alternately, you could also freeze the roto work, then apply the roto layer as an alpha track matte above your source layer that has no effects applied.
The rotobrush is actually 10x more effective with some kind of enhanced contrast / levels in the effects stack before it, as it picks up the edges and pixel changes better, in my experience.