Unmap your escape key, that will force the habit. I did this when I moved my control and meta keys to the left thumb of my kinesis keyboard, and it helped train me not to hit the old keys.
Under OSX I used a tool called KeyRemap4MacBook which adds an item to the control panel that lets you reconfigure keys. I just tested it, you can can disable the escape key, but Ctrl-[ still works like you'd expect.
