I know the oil separating is a wives tale but figured it couldn't hurt lol.
I'm sure oil is heavier than methanol and I'm sure if you gently filled a fuel bottle with a fuel pump or crank by skimming the top you could get lower oil content, it may not seperate, but could settle IMO.


Also you said basement, sitting on concrete is a bad place for fuel because it can promote condensation - (I believe that is the reason for this idea).
A piece of wood under it would help because it's porous and don't get as cold (or transfer as much cold) as the concrete.