It would be nice if fuel consumption showed the actual LFSWorld fuel usage, unless combo never driven before. Or just a buttom that gets it off LFSWorld...
Go to pits.
Go to the INFO screen.
There on the right, just above the fuel percentage, it says how much fuel one lap takes.
Multiply it by the number of the laps you are going to drive.
Add a few percentages to be sure.
You are ready to go.
I've seen this suggested before and I don't see why not. Maybe not related to the LFSW stuff, but just a record of your fuel-lap the last time you used that setup would be handy.
You can't tell me that real teams don't write that kind of stuff down during testing