I think that practicing the skill is the proven method: look at how England won the Rugby World cup in 2001 against Australia. The penalty kicker Johnny Wilkinson spend hundreds of hours visualising kicking the ball over over the goal, and then kicking the ball over the goal. His routine was to visualise and then do. AFL players do the same thing when they get a free kick near the goals – visualise then do. Ice hockey players do it before a shoot out – they decide what they are going to do, visualise it, and then do it.
I assume that penalty kicks would be the same. practice the action of visializing and then doing. During practice you can include recorded crowd sounds; get players to jump around behind the goals to distract the kicker; set up practice netting on the goals to focus accuracy (like ice hockey players do); go to other major sporting events and practice centering the players with large crowds around them.