Nationalization
There should be something that increases your culture in occupied territories or colonies. What do I mean?
Prussia undertook a vast program of Germanization or Prussification if you will, in Poland for several decades, increasing the number of citizens who felt more German, even though their roots were Polish. This was also true, with Russian attempts at Russification of Finnland and their other Asian territories.
I guess I think that there should be some sort of a button that instead of creating a factory, you increase the number of teachers of the national language that would bring more people to the views of an Imperial power.
After all, I don't think that if Prussia (Germany) takes over all of Russia; doesn't mean that they will stop the building of all factories in places like Vladivostok and further reaches of Russia.
I agree that it might take 2 to 4 decades to make the Russians in these provinces begin to think of themselves as Germans, but if you have the cash to educate your conquered people, you should be able to be rewarded with the benefits of increased output.
Just a thought, but I do think it is reasonable.
My proposal is that a phantom factory is built and for every year that this factory is built you get 3% of the population becomes your national population. Which means that it would take roughly 33 years to Germanize, Russify, Francify a certain population.