Replace that little voice with a jingle that sticks in your mind from TV or a favourite song.
Part of Elvis's promised land has taken me to few pretty effortless wins in competition.
I personaly belive that if I had to "work" at shutting out distractions,,I probably couldn't do it,,,,,,but by turning a simple song or jingle into a mantra,I don't need to "work" at it,,,it just happens because I've replaced the voices.
I've said it in the "I just missed again" threads.You can't think of more than one thing at a time,,so in this case intensionaly repeat one very simple thing over and over in your mind,and just let your shooting happen.
After all,the skill is already there and we just need to let it out unhindered by interfearing thought.