Can't Set Fuel Tank Consumption (Normal Flight) Priority

So I’m trying to correct the fuel consumption/tank priority in a 3rd party plane. It’s a very simple design in which both wing tanks, via mechanical pump, constantly feed the header tank which gravity feeds the carb. Thus, the header tank stays full until the wing tanks are exhausted.

However, I simply cannot figure out how to configure the sim plane to consume fuel in this manor. No matter what I’ve tried (via SDK) consumption is from all tanks simultaneously.

Help?