The cheat/bug/exploit works in the following manner.

You will need at least one availble free tile and some cash on hand (not much 100). This method is only good to build instantly items that cost more than 100 (suchs a industry centers and other high end items which run in the 1000's)

1) Build the social item you want (bank,factory,research center ect)
2) Now build a farm or other low end item on the spare tile but go ahead and purchase it.

What occurs is that your farm (or other low end item) is not allocated to the free tile. Instead when you purchased it, it builds whatever item you were currently building (for the cheap price). You will only be able to do this one turn at a time and will work even if you dont have any resources to social production.

Consequently if you do the reverse say.. buy a research center and a farm is in the build queue you just spent alot of cash for that farm (call it Union dues).

If used correctly you will never have to put any resources into social production you can just buy all the social improvements for a cheap price.
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Note: You will only be able to use this "feature" once per turn