Monopolize keyboard for InputField (uGUI) the same way it works for TextField (IMGUI)

This question has a long history which goes right to the Unity 4.6 beta, and it still has no answer. I saw several workarounds, but all of them included an enormous amount of kludges all over the code. All of them required to manually check that no InputField is currently selected every time you want to process the input. Some people advise to do it in the centralized singleton, some prefer to do it independently all over the code.

The problem is, the old IMGUI system does it! It just works for TextField: as soon as you pass the focus to the textfield, all the inputs get reset. How can we get something like this in the new uGUI?