That's why i posted it
The biggest problem, IMO, is the lack of distinguishable ranges given for each button combo. During my trial run, i tried to make a spreadsheet that gave predicted resistance readings. I was hoping that, once finding R1, R2, R3, R4, it would be trivial to calc R1+R2, R1+R3, etc for all combinations. No dice. If one of the pre-assembled vendors here wants to change their design to allow more ADC, I would expect them to do their own R+D for their optimal resistor values.
I kinda think in retrospect, that it would be cleaner to do a simple 1-2-3-4, single resistor per button, and use the LongPress flag to assign special functions to each of the 4: such as: LongLeft= Save Tank/Trip to EEprom, LongRight = Clear Tank/Trip, LongUp = Setup Menu. Either way, the basic code foundation is there, for single-resistor or ladder-resistors.
Also, we could get even one more ADC, if we changed the VSS over to a digital pin. I believe that analog pins 4+5 also can be used as a two-wire serial interface (TWI), so that opens up other expansion options as well.