To extract ether from a spray can, I take a jar of appropriate size and punch a small hole in the lid. Swap the nozzle from your quick start to a nozzle that has tubing attached,,, like WD 40. Simply spray the ether into the jar with the tubing inserted in the hole. This releases the propellant and allows you to extract exactly as much ether as you need. No waste and the ether you don't need stays safely in the spray can for the next time.

Ether loss in fuel can be eliminated by making up a mix of just oil, kerosene and additive ahead of time. I use a 50% ether, 24% kerosene and 24% oil mix along with MEKP for the additive at 2% for my general fuel needs in small engines. The pre mix is 48% kerosene, 48% oil and 4% MEKP. I fill up my fuel bottle to nearly the halfway point with this mix and then spray in the ether directly into the bottle till it's near full. This gives me my fuel for the day (1/2As) and I seldom need to take any home with me. This prevents your fuel from ever going stale due to ether loss which is really bad news on small engines, I've found.