I put it in a separate, password-protected .mdb altogether that the users aren't even aware of, called AllowDisallowShiftKey.mdb, since I, as the programmer, would be the only person who would need to disable the shift key in the main application (for quick code changes/fixes).
This .mdb has a log-in screen, and one screen with two buttons: Enable Shift and Disable Shift. Works like a charm. Let me know if you'd like a copy.