I'm asking specifically in the context of conveyer systems but the same thing would be nice for a distribution office as well.

I currently have a coal power plant being fed via conveyer from an aggregate storage facility. I have a second conveyer going to a shipyard to export excess production in addition to selling spare power.

Without any way to prioritize distribution I am running into the following problem...

Option 1: Insufficient throughput on the export line. Slowly the aggregate storage fills and eventually the production jams causing unemployment and loss of potential income.

Option 2: Excess throughput on the export line. Without priority to fill the powerplant first in this situation I end up starving the plant. Without the ability to dynamically switch power import-export option this also kills the power to my republic and that's bad.

What I am looking for is some way to tell the game to keep a certain factory or facility filled always and then pour the excess resources elsewhere. This would alleviate jamming up the production lines.