I don't tie them of anymore. I just use Krazy Glue for wood and leather. I found out some years ago that if you finish off the fly and leave the hackle out making sure there is thread on the post were the hackle will go you can just use the Krazy Glue. Just put a drop on the post take the first warp high up on the post and then two more below that one coming down toward the body Hold the hackle on the off side and wait for a few seconds and then clip of the extra hackle from underneath and you are done.
It will take tying a few to get the hang of it but when you do it sure makes tying them a lot easier on a person. And yes it will hold well if done right. I have taken as many fish on a fly tied like this as one tied the regular way. I have had people I taught this to tell me how much they like doing them this way. Ron

PS: I have tried several glues and the Krazy Glue is the only one that will work as it should. And it has to be the one for wood and leather to? Don't ask me why? I think it has to do with how this glue is made? But it holds it real well.