I'm aware of the non-fouler trick. In this case, the moron that replaced the engine in a new customer's '02 F150 (4.2L V6) a few months ago cut out the cats and the downstream O2's, replacing them with several feet of flex pipe clamped at each end. (Yee haw, welcome to Kentucky.) The expense of new cats is out of the question for him (he could barely scrape together the money for me to do intake gaskets) and with the downstream sensors completely gone, a set of eliminators is half the cost of two new sensors that are just going to get non-foulers put on them to keep the CEL off. However, the local exhaust shop (going to put some proper pipe in place of the flex for a good price) won't do the pipes unless they put sensors in them, claiming it'll ruin the engine shortly if they aren't there.
I just wanted to know if I was under the wrong impression about the function of the downstream sensors or not. It appears I was correct.