I think the hard part of testing would be finding someone with diabetes with uncontrolled blood sugar. Those are going to be the folks that will show the greatest fluctuation in the fastest time. However, those are also the folks that many "external" factors also affect them easily. Would be hard to tell what is really causing the jump. While uncontrolled I can bounce 100 points Thinking about a life saver (okay okay, a stretch) but there are just so many variables.
Being that a fasting blood sugar should be 90-100, and about 180 (Max) 2 hours after eating (rough guidelines), I would wonder what a significant jump would be? I would assume it would be best to do a 12 hour fast, test, and vape for x amount of time, then test again right after vaping, and two hours later? Or maybe the two hours is digestion time for food. Hm.... this is interesting to think about.
All in all I am not too worried about it, but its and interesting thought expeiment to think how you could test this without a lab.