I'll assume its got the 20% oil which is normal for heli fuel.

Mix it with 2 gallons of 10% 4-stroke fuel, with appropruiate oil content. You'll have a bit over 15% nitro, and the castor/synth mix normally found in 4-stroke fuel will mix fine with the synth oil from the heli fuel. Cince the current O.S. recommendation is 20% oil with a portion being castor... should end up just about right.

I run 15% heli fuel in my O.S. 91 FS when I can't find other fuel with sufficient oil content. It seems to like this better than normal 4-stroke fuel. But I still like to have some castor content... (and the engine maker specifies it needs castor)