Anyone noticed? The Mongols are running 30% lux... So the AI does use the lux slider quite ok, doesn't it?!
Regarding the problem on how to still beat them to Hoover's: I once used the following trick in a similar situation, when I was about to lose the race for an important wonder by just 2 turns: I gifted them Monarchy. Surely enough the following turn they revolted (even though they were already in Republic...) They got 4 turns anarchy -- after which they chose Republic as their new government...




Of course, those 4 turns anarchy were enough for me to pocket the wonder...
Anyway, I think this is quite predictable: many times when the AI gets a new government tech, it first revolts and only afterwards asks itself the question of whether it actually
needs a new government... (Perhaps this is also influenced by the preferred/shunned governments of each civ?! Might be an interesting field of future research.)
So if you manage to research Communism/Facism in the remaining 18 turns, you could gift it to the Mongols... Chances are you'll still get your Hoover Dam.

You can increase these chances by involving them into a couple of wars: it is well known that the AI shuns Democracy and loves Facism, when things get rough.
So a plan of action might look like
- get Facism asap
- gift it to the Mongols
- if they don't revolt next turn, declare war
- and sign as many alliances against them as possible
(If they already know Facism, steps 3 & 4 may already give you good chances that the revolt.)