Enable allocation from conveyor belts

Add or enhance conveyor components that can *allocate* inputs to outputs. e.g. 60% goes to port 2, 40% to port 3. Scenario: I have a crusher turning rock into gravel. It makes 24 gravel on each cycle. I would like to send 8 units of gravel to another crusher (to make manuf. sand) and 16 units to storage. Perhaps this could be a modification to the balancer or sorter. Need for the U shaped conveyors but would seem to be a good enhancement for the other conveyor types as well.