Mine keepers sometimes land in the middle of a 3-exposure 6x6 120 strip, which makes it nigh-on impossible to manipulate the strip in my negative carrier. If the neg on either side isn't a keeper or technically duff (underexposed etc) I tape a strip of light card to the strip. Otherwise I just have to live with it. Its rarely a problem for me with 35mm because I cut into strips of 5 which sticks out from either side of the carrier. Sailor Vee...

Cheers,
kevs