We've been using modified iaijutsu rolls (OA) for snipers. Same basic mechanic; has to be a surprise round (just keep making that Hide check), opponent has to be flat-footed. Roll the skill before the attack. 10-14 gives a +1d6, with the progression increasing 1d6 every 5 (maxes at 9d6). You are also flat-footed for the round you're shooting.
It's worked very well. Just enough random elements to not make it game breaking.
