It annoys me slightly that you never see this discussed in talk about high level equilibrium traps, but the difference between Europe and China in this regard is that China was able to successfully close itself off from global trade networks, while European sovereignties were far too fractured and multitudinous to ever accomplish the same thing.
Europe is quite fractured geographically and demographically; if one did want to arrest the general drive toward both technical and social innovation in Europe I'd think a necessary but not sufficient condition would be for someone--Holy Roman Emperor, the Papacy, some other monarch--to achieve comprehensive and lasting conquest of pretty much the whole subcontinent, at least as far eastward as all the German-settled regions and possibly having to go so far as to subdue or otherwise induct England into the continental system. And the Scandinavian countries, and Iberia (unless Iberia stays Moorish-ruled and thus perhaps outside the European system).
It seems like a much tougher hurdle to jump than unifying China; of course China's unity may be more an artifact of the feat having been accomplished thousands of years ago than any natural geographic unity.
Anyway--necessary, but not sufficient; the regime would then have to still have an interest in promoting stability at the cost of economic progress.
But without unity, what you have is a bunch of smaller states in competition with each other, with a merchant/financier class pretty free to gravitate toward whichever regimes offer them the best available deals, thus all rulers had an interest in both keeping these classes reasonably happy and in at least matching, if not outdoing, the innovations of their rivals. Some got good at it and survived, others belatedly compared notes on the examples set by their more successful rivals and rallied; as the situation kept changing the winning strategies of yesterday became the backward conservatism of today and the pot kept stirring.
I mean, it's not like most of European culture in the relevant time period wasn't extremely conservative and anti-innovation -- right up until the industrial revolution itself Luddites would engage in machine-breaking. The difference is that the high level of inter-state competition prevented this attitude from actually attaining and keeping power for any long period of time.
We agree on the role of competition, but I have to point out--Luddism wasn't a perennial conservatism of the countryside; it was a radical reaction precisely to the industrial revolution as experienced in the countryside. Earlier peasant revolts were not against industry or technical innovation as such; they were against the manorial regime as such.
If I were going to point out reactionary culprits in the medieval and early modern period, I'd be looking considerably higher up the social ladder.
In order to keep Europe backward and undeveloped, you need to stop the commercial revolution of the 12th century. I don't know how possible that is. The Mediterranean is such a natural highway of commerce that you would probably have to get rid of it in order to actually succeed in stopping some kind of commercial revolution.
Again--even without the Med trade, which was very important of course, Europe was quite a dynamic trading region. The Rhine was a major avenue, as was the Baltic. I honestly don't know to what degree these channels were stimulated by carrying trade originating in the Med region or beyond it, but I would think that even if the Mediterranean turned into a sea of poisonous boiling mud, north of the Alps there would still be a lot of trade between regions of northern and central Europe.
So I'd think we're left with scenarios either of some great, eternal, and ultra-conservative Empire, which is tricky to imagine how it could rise and sustain itself, or with drastic climatic, epidemic, or geological disasters essentially devastating Europe and driving the units of population left that can cohere down far below the level prevailing even after say the Black Death or the Thirty Years War.