I've never run anything like what your trying to do, but I like the idea (I can
think of one GURPS module, "Unnight", that deals with a colony that has been
seperated for so long, and got off to such a bad start, it degenerated to a
TL2-3 society, except for a few, called the 'wizards', who possess some higher
technology). There was an issue of Challenge that had an article dealing with
using drugs, psionics, and other things to make things appear as if they were
done by magic. Can't remember the number offhand, but it was a special Horror
Issue.