NOS Injected into Scale engines
NOS doesn't ad "power", it ads oxygen. The extra power comes from the extra fuel you have to burn to get the air/fuel ratio back to optimum.
On NOS equiped cars, there is a valve that dumps more fuel when the NOS is activated. You'd have to do the same with a model engine or it would go lean instantly when you hit the NOS. If you had lightning reflexes and an inflight needle, you might get lucky one time out of 10/20/50??
On a glow powered engine, the only way to control the ignition timing is with plug heat, fuel composition, and compression. As soon as you dump all that extra fuel into the engine, my guess is it will start to pre-detonate. On cars running NOS, they have spark ignition, not glow, so they are able to control the spark advance. You wouldn't be able to on a glow engine.
Also the AMA safety code says that only air at atmospheic pressure can be used. Sure, not everybody is an AMA member, but I'm sure you'd see "NOS set-up for your plane" ads. You said you Googled them..I've never seen one advertised or used/
Boater has it in a nutshell...nitromethane does the same thing (ads oxygen to the fuel) as NOS, and it's a lot easier to implement on a model engine.