they do make wide jigs, but a lot of shops may not have them. even in Mammoth, which is somewhere that seems like they would be mounting a lot of fat skis, they had to freehand my Made'Ns. (Maybe it's just because I went to P3.)
Get 4" wide strip of plexi. Scribe center line on it - in the center
Put boot in jig and adjust to boot size.
Clamp jig to plexi with short section of 2X4 underneath just like a ski.
Mesaure with mm ruler and mark vertical and horizontal centers on ski with pencil
clamp plexi down centered on ski
drill ski using template as guide
screw down clamps