I made them back to back, one regular and one simmer, and did one test. 1/2 ounce in each burner. Set it down on a sheet of silicone rubber to seal the bottom "simmer" burner while the regular burner went it's coude through the 1/2 ounce. No vapors were noticed coming from the bottom burner. I tested it occasionall with a lit match touched to the base edge. I tried turning the unit over when the top burner was almost out and whooompfh, the bottom burner lit instantly with a large amount of flame. condensed fuel was on the silicone pad aflame :-) That was a shot of adrenalin :-))))) So, the unit would have to be fueled one at a time.
It took a long time for the bottom burner to heat up to a point of not being able to hold onto for very long. I think I could have had a lid on the bottom burner while the top was boiling water. Blow out the top burner, turn over, remove lid and then light. I'll have to try that tomorrow.
Photobucket video, click on photo to view: