Brilliant Idea: Portion Plate

On my incredibly annoying drive home today (charities are stalking all the intersections...again), I randomly came up with the idea for a portion plate.  It is not really a plate per se, but an overlay that people can put over their plates while they are doling out their portions.  There would be sections for protein (size of the palm of your hand), starch, and vegetable. It would give weight watchers an easy guide to what the size of their meals should look like, but would be removable so they an eat their meals on a normal plate.  And of course, it would be collapsible for easy storage.  Maybe there would be a secondary type of tupperware so you can have the correct portion sizes for lunch the next day - the lid would also help limit the height.  What do you think?  Is there something like this already out there?