Fuel Management?
What is wrong with the method you have been using to date? The gauge system in the 135 is very accurate. It even accounts for the aircraft attitude. You can change the units from the front end of the VEMD.
The fuel management system uses flow meters. I can't understand why it was done this way as the data is available from the EECU, which would have been a far simpler solution and accurate enough. The A109E/S does it this way.