If you're just worried about holding down left control, just goto create new command and under "key presses" click the "release key" button and assign it to left ctrl. alternatively you could set up another key to hold the button down using the same method.
edit: i might have misunderstood you originally, but you could set it to have TTS(text-to-speech), or a sound effect, remind you everytime you press control, or toggle it to hold it down and tell you its down or up, and remind you.