I used to have the same problem, storing gas/oil mix for my motorized bike. Now I simply carry 2 oz oil in my reserve bottle. If I'm at home and need gas, I close the petcock and pour oil into my four-liter tank. Then I pedal to the nearby gas station. By the time I get there, the oil has mixed thoroughly with the 8-16 oz gas im the tank. I simply pump three quarts of gas into my HT tank and pedal away for one block. Then I open the petcock, start the engine and motor away.
If I'm on the road and need gas, I pull into the Chevron station, add oil then gas, and motor away. I've been doing this for a few months, with no protest from the engine.