Build a Butch strong frame with a press in the center, and solid mount points to secure the leaf and so you could duplicate the amount of arch you put into the leafs. It would cost more than a set of leafs to build, and it would only work half-ass. So, I'd just buy new ones, or send them out to a shop who can do it right.
Plus metal fatigues. Yes, a rearch at a pro-shop could very well cost less than a new leaf pack, possibly even less than an Add-a-leaf. I personally find that AAL's and re-arches on worn-out spring are a band-aid fix. My experience with them is that they wear out and are back to flat significantly faster than a new leaf pack. Plus of the three re-arches I've been party to, one of them cracked the leaf the second time around, rather than just wear it out normal.
So I agree that doing it yourself is a bad idea all the way around. Sending it to be done or using an AAL is acceptable if you're strapped for cash, but be aware of the probably consequences.
I will say that, in the possible chance I'm about to be flamed, that my experience with AAL's and re-arches were all on full-size trucks. Mayhaps there is a significant difference w/ our lighter trucks, but I would guess not.