Although I wouldn't mess with the sear at all, I don't recommend it either.
On hennings website he has a pretty detailed video on how to totally dissamble a Witness. If you got the trigger bar out polishing the sides should help alot.
On my Witness I simply polished the top of the plunger without dissambling anything. A real quick touch with a fine dremel tip, made a big difference. It was causing hang ups in there. I always put a drop of oil on the sides of the trigger bar also. Seems to keep me happy.
I would like some trigger work done on my Witness as well.
The website you linked to Detroiter was interesting, but I'm not handy with those type of tools or interested in learning how to use them to fix the trigger myself.
Dondavis3, I would think a certified (and hopefully) qualified gunsmith could do the work. I wouldn't think that a Witness is very different from other guns and a good gunsmith with quality parts could vastly improve the trigger action and pull.