Cool! This is more fun than running a factory this morning...
Getting nearer now. Your weight/ ff table gives fuel flow AT SEA LEVEL - i.e. it relates alt and weight effectively. Did you get the equation for the line from Excel? Just wondered as the line can be approximated to linear when plotted, which will make further calcs a little simpler. Will need to error check that though.
Anyway, what I need to know is the WEIGHT at which the Alt/ff table was calculated (I assume Max?). Then it will be possible to relate a ff increase to a weight increase and build up a matrix of FL/ Weight/ ff. Once we've done that, Excel should be able to sort out what you want.