Only way to actually deter,ine insulin sensitivity at all would be to monitor blood levels every 2-3 hours every day for about 2 weeks along with keeping a detailed journal of what you eat and when. THe doctor can then do an analysis to determine how much insulin you need to increase BG levels.

This is what is done during diagnosis and treatment of diabetics.

Problems of course are :
1. Doc will give rec levels for a diabetic, not a bodybuilder.
2. average BG levels will be VERY dependant on what you eat and so will change over time .