This is the way I do it too. Took me a long time to be able to do it myself, I used to net them and get hubby to do the other bit. He'd take it away outside so I couldn't see or hear what he was doing. But I can do it myself now, still sad for me but you just have to get beyond the killing part and realise that you are doing the best thing for the fish by ending his/her misery.
Speaking of which, if my skinny zebra loach doesn't cark it while I'm at work, I'll be euthanising him tonight when I get home.