You can use Paint on a separate layer set to be a track matte. (Here's a page with some alternatives to Vector Paint.) Also any earlier comps with Vector Paint applied will still render correctly.
However, there are much better methods for masking a layer in AE (also known as Rotoscoping) Check it out here.
The vector paint as masking goal is to draw any precise/in time animate able/ line on in real time visible background. I have no reason to draw in separate layer even since this is set as a track matte - theres still no control, I must see what I do/draw. In my case the only solution is to use some plugin (trapcode). No more options inside AE. That's a shame. Rotoscoping is fine, but in smooth/animated line case this is not a solution.
The page that Szalam pointed to recommends a way to do rotoscoping that achieves your goals:
Lock the layer that you want to rotoscope. Make a white solid layer; turn its visibility off. Select it. Draw masks on the invisible white solid layer as you use the visible but locked footage layer beneath as reference. Use the white solid layer as a track matte.
This is how most people (including me) do rotoscoping. It works quite nicely.