I just tried out BA's gluing method (document at http://www.angelfire.com/zine/digest/baglue.html), wherein you put a little piece of tape in the middle of the unit, and then temporarily tack the unit down onto your head using only that little piece of tape. Then you glue the front half of the unit to your head, remove the little piece of tape, and then glue the back half of the unit to your head.

I'm here to say that it works famously!

It's still takes me more than three hours as a relative newbie to remove my unit, clean my unit, clean my head, shave my head, dye my hair, reattach the unit, and do a few glue touch-ups, etc. But since I only have to do this once a month, the time spent is not that bad. (I only have to do it once a month because my glue attachment lasts two weeks with touch-ups, and my stylist does the other attachment for the month.)

I'm not sure that BA's method saves me time, and I did end up pulling out a couple of hairs removing the tape, but it sure saves me a lot of stress worrying about whether I'll get the unit on straight or not. Also, I think I do get the unit on straighter.