OK, update on the experiment of using hookah Shisha instead of pipe tobacco for making essence, per your directions. First, you apparently CAN'T let the VG get too hot. When you do, on a gas stove, the instant you put shisha into the hot liquid, it will ignite like bananas flambe' and the smoke will fill the entire room...
Luckily, I had a lid and was able to put out the flames instantly. The shisha didn't actually catch on fire--it must have been the vapors from the sugars that lit off, or else there might be alcohol in the shisha (the flames were pretty blue...)