I haven't been inside a controller to know, but it should just be a matter of replacing the switch they are using (probably a normally open, or off kind) with a normall closed, or on kind.
That way it could be used more properly as a brake, eliminating the need for holding the button down all the time.
well i found a site, it says to remove the two wires that are soldered to the positive and negative terminals and solder them back in reverse. but it was in german so i couldnt understand the translation so i didnt do it. just wondering if someone has an english version i can read. i seen it before just dont remember where tho