I figured out how to do this with some PNG's, and EFF and SEXP's and table edits.
Set up a new custom gauge in your FuelGauge-hdg.tbm, set it to use a custom graphic such as col_miscbargauge_fuel.
Now have an EFF file with say eleven frames if you want to keep it simple. Make 11 PNG files with the same name col_miscbargauge_fuel_0000.png through 0010.png and edit the graphic to reduce your fuel by 10% each time.
Then you can use the variables that were set up earlier in a mission to read FuelQuantity and have it display a graphic each time a <= value is reached using the SEXP set-hud-frame.
In this way, as the variable is reduced once it reaches each threshold a new frame is displayed until the variable reaches <=0 which displays the 11th frame, out of fuel. If you want it more complex, add more frames to the EFF and create more PNG's.
In my test example I had the FuelQuantity variable set at 30000 which at 100% throttle is 300 seconds or five minutes worth of fuel. In the one SEXP I'm reducing the variable by the throttle setting so this will vary fuel consumption based on your throttle setting/speed. Then there is a When SEXP checking for every 10% drop and changing the graphic to the next frame. This simulates the fuel bar dropping. You also have a readout of actual fuel quantity divvied by 100 that you can place wherever you like on the hud. I have it below the fuel bar.
And lastly, what happens when you run out of fuel. Force Glide, Player use AI, set goal playdead, show a message you're out fuel, kill glow points and thrusters, then after a delay, end mission fade out ect.