Well, it adds vicsocity to the mixture, which means it would stay in suspension a lot longer after you shake it up. That should pretty much eliminate any question of uneven dosing as a result of settling too quickly.
I dropped by a local compounding pharmacy today and had a frank discussion with a pharmacist there. Told him what I needed and why. He said propylene glycol would indeed be the right stuff, but couldn’t sell me any, and couldn’t legally make up a mixture for me.
It’s available on eBay in food grade, which should be right. An 8oz bottle is less than $10 including shipping in the US. That would last a long, long time. It would probably also make sense to mix in some alcohol as a preservative, as in your example.
At that price, I’m going to go ahead and order some. Next - where to get bottles. I’d like to mix the entire 2 grams at once, then refill a 20 ml vial from that as needed - I have some that size left over from Kits orders.