A whites trigger stop is helpful with guns that have a long trigger pull. A whites trigger stop is simply a soft piece of rubber similar to a pencil eraser either glued on the trigger or on the frame behind the trigger. When you shoot the gun you pull the trigger until it touches the rubber, aim and squeeze a little more. I put a trigger stop on a Kel Tec P11. It is much easier to shoot with the trigger stop.
Anything else I know of that will shorten the trigger pull is sketchy and not advisable.