What types of things are you scripting? Is it truly on the fly or are there a few different autonomous modes you are trying? If it is only a few, you can look into just having radio button selection of autonomous mode with the SendableChooser:
http://wpilib.screenstepslive.com/s/...smartdashboard.
Otherwise, you may be able to just make the textbox bigger (longer) and make a custom shorthand. d(60), t(45), f could be input for drive 60 inches, turn 45 degrees, and fire. Not sure how complicated you are looking to get though.