Just downloaded and installed the software from
http://www.obddiagnostics.com/ProgWin.html . You can operate it in "simulation" mode without the hardware (random values).
Pretty neat. But I can see how I'd like to improve it already.
It does have an instant & averager resettable MPG function, based on either MAF or MAP output. But this function is pretty basic compared to the SG, and I'm not sure it can be fine-tuned (e.g. distance & fuel used calibration).
The guy who sells/writes this lives in TN. I bet he'd make some cash if he got involved at GS and expanded its MPG functionality. He could be a real competitor to the SG2.