Attempting to unbind player controls.

I wanted to set a custom GUI using the inventory key bind. Almost right away, I encountered a number of problems I couldn't solve without learning Java. Through pretty aggravating trial and error, I found a solution to my problem, which was to unbind the default inventory key (E), and reset the key binding towards a procedure to open the custom GUI. And with how close I've gotten, I really don't want to give up on this solution, though there is still one roadblock. In the perspective of the player, I am forced to manually unbind the E key so that the GUI I am working with can open properly. I think the two solutions I'd be most acceptant of would either to find a way to unbind the E key automatically, or to bind a procedure to the pre-existing default E key binding. If anybody can help me solve this problem, I'd really appreciate it!