I don't advise doing this, but it's been working well for me for several months.
I mix oil and fuel @ the gas station. If this method was good enough for Yamaha mopeds decades ago, it's good enough for me.
I started using Opti-2 oil for the last three 4-liter fillups. An ounce of Opti-2 is stored in the 18 oz aluminum bottle in my bike's cage.
When the tank is down to 6 oz or so, I shut the petcock and add oil. Then I pedal to the nearest gas station and add 3 quarts of 87 octane gas. I usually pedal for a block, then stop and open the petcock. Then I start up and motor away.
No adverse effects so far. The Tanaka engine runs better than ever, and its sparkplug tip looks chocolate brown
I'm also assembling my own oil-dispensing system. A measured amount of Opti-2 gets pumped into a clear reservoir atop the fuel tank. At a designated time, the oil is injected into the tank. Then gas is pumped/sloshed in @ 100:1fuel/oil mix.
I'm not recommending my method to anyone. JMO, a good/satisfactory mix CAN be done at the gas pump.