One hack way is to map the TAB key to pause the game along with the "P" key (hint: "Input (General)"). Map both keys so if you ESC out of the menu, you still can unpause the game without bringing up the menu again.
However, I agree with SirPoonga and don't think this is a good idea. If you remap some keys (ctrl, alt, space, numbers, arrows), you won't get the true key mapped ("left ctrl right ctrl" instead of just "left ctrl").