It should work fine to just cut your 10/20 glow fuel in half. Then use THAT to mix with 2 parts of high test gas. I usually mix up three quarts at a time.

So, once again, mix one gallon of your 10/20 glow fuel with one gallon of methanol.
Then pour one quart of that into a fresh jug, and then add two quarts of high test gas. Let it sit for a while to be sure there is no separation, then go for it.

If the rpms drops significantly when the engine is warmed up and you remove the glow plug power, you will know your mix is a touch light on nitro. The next time then, you can mix up some fuel with the methanol and 20/20 glow fuel.

Good luck Jim,
AV8TOR