Please stop building overlap there is no place for it in the game. Possible solution make some of the structures smaller.
Actually it does not completely fix it. You cannot place a building's plans on top of a currently existing or partially constructed building, however you can queue up plans on top of other plans which fabs have no problem building. Using this method you can still stack as many buildings are you want on the same spot. Edit : Also, some of the building hit boxes, like the mex for example, are quite small and can still partially overlap other buildings. Two mexes can be built about half on top of eachother.
ya I just spammed a million buildings in one spot and sure enough still works just fine. Needs fix (version 49900) http://i.imgur.com/ciEhSj4.jpg
You don't need to do anything fancy, just spam click. It only doesnt work if there is already a building built there but you can queue up buildings to be stacked.