I was thinking along these lines : have a close look at the hlder you already have. Get some of the black plastic document holders found cheply in office supply stores. Have at it and copy the deign outer measures identical, but opening for negative strip adapted to the smaller 16mm film. Try your best to copy the design so that you have a lower basis for the film and an upper holder, never mind openings for each negative, like in the factory designs, or if some form of holder is desirable to keep the film as flat as possible, just leave one single mm and place the negative stripp accordingly.
I have my strips cut and stored in ordinary 24 picture negative sheets, i.e. strips of four 35mm negatives length, I would make a a6mm negative holder accordingly.
I will have a go at this after summer vacation, but my scanner is a Canon 8800F, since I scan 6x6 also.
PLustek : there are several brands of these simple copiuers entering the market, some have, some dont have 110 adapters, and those that have seem amazing there must be a market for 110 out there, somehow.
The last copier I looked at had a resulution of 5 MPx interpoled, which means a little over 2 MpX ( ca1920x1280) in real terms on a 24x36 negative, that leaves precious few pixels on a 12x17 negative and even less on a 10x14....
The maker of that last one stressed their product was NOT a scanner, but a copier........