I agree. The difficulty with using cultural means to stifle invention is that you usually wind up with societies that don't line up with what you want, anyway. If the goal is a medieval-style civilization with a millenia-long history, then you don't have a lot of wiggle room to play around with culture and economics. Of course, you're not limited strictly to the medieval period, either, as many fantasy civilizations fit quite well into the late classical era, also.

At exactly what stage do you want to arrest progress? Simply killing the printing press might do what you need all by itself, although many fantasy societies have a ridiculously high rate of literacy in comparison to medieval Europe. You could also modify Boyle's Law: decoupling the relationship between the volume of a gas and its pressure disables most engines. That, by the way, is one of the story points of Stirling's Dies the Fire novels, which might be worth a read in this context.

Oh, and it suddenly occurs to me to suggest looking at Japan, which had an extended period of technological stasis. Part of that was due to their isolation, of course, but what prevented them from independently entering an industrial revolution of their own for so long?