Variable rice dispenser

Rice dispensers already exist (mainly available through asian export companies as far as I can tell from a search on the web), but they all seem to give you pre-defined measures (one cup, or multiples thereof in the fancier models). For one thing, one standard (american-standard) cup is slightly over the odds for my taste, and depending on who I'm cooking for, I may want larger or smaller amounts. So, I'm imagining a dispenser mechanism rather like an optic for spirits, made of clear plastic with some kind of movable bit with which you can control the amount dispensed. The dispenser should also have volume markings on it so you can tell exactly how much you're setting it to (in fractions of a cup, fluid ounces, and centilitres, just to make sure everybody understands). The dispenser would have to be designed differently from a standard spirits optic, in that the rice doesn't immediately flow down into the dispenser after a measure is dispensed (because if it did then adjusting the size of the dispenser would be difficult with the rice in the way).

Another thing: I don't get through that much rice myself, so I don't need a dispenser with an enormous holding capacity, like the available models all seem to have. So a smaller dispenser, which would be light enough (even when filled with rice) to hang off the wall to save worktop space in the kitchen, would be great.