One way you can clear the EV's is to get a plain white "reset bag" from punching the default punching bag. Usually takes me about 5 or 10 min to get a reset bag. If you don't want to get multiple ones you can just get the one, save then use it on a pokemon, calculate the IV's then soft reset and do it to a different pokemon.
Also you can grow berries to reset the EV's although IMO that takes up more time. after either of those it should be easy to come up with the IV's on a calculator