FYI it's an aerosol can of ether starter fluid, which its intended purpose is to be sprayed into carbs to get engines to start. There is literally no way to do this other than how the guy in the video is doing it.
Your concern for safety is rather laughable for the size of the engine he's doing this with. Ether if improperly stored is the most dangerous thing as a can of 50% either having crystallized is a good few grams of TNT equivalent, which would make it a small hand grenade. (however an aerosol can with peroxide inhibitors in is extremely low risk if its new)
Talk to anyone who has worked in a mechanics garage and this video is extremely weak tea. Try being near a V12 when you've just filled every spark plug with ether and you're spraying it into the air intake. Now that'll give you an uneasy feeling like you've just made a potential bomb, but the fact of the matter is that the failure points in engines are valves and gaskets long before any metal part fatigues and becomes dangerous.
His piston chamber appears to copper piping, which don't fragment they split, so there's really no risk there. Think bronze cannon over cast iron.