Good to see I'm not the only nutter doing stuff like this (well not yet, but I intend to).

What I've got so far is a pinhole camera that can fit about 11x14 (possibly bigger, haven't tried yet).
But paper is paper and paper is slow, and I've got a whole lot of film lying around, 135 and 120. What I intend to do is to cut up the film (maybe 1 or 2 rolls per photo) and tape it to the back of the camera. Proper alignment isn't an aim of this, I intend to have overlaps and gaps between strips of film.
Of course, I could just scan it and digitally arrange (why not, I've got 20GB of RAM to fill up), but that's boring, I also want to contact-print.

My question is, what's the best way to hold all the negs in place when contact-printing? Because of the weird alignments when shooting, I'll have to arrange them in the light and hold them in place before upturning onto the paper in the dark.

I was thinking of clear-plastic-adhesive sheets (we aussies just call it Contact, like you cover schoolbooks with to stop them getting ripped), but then the negative might stick to it too much and the emulsion could peel off and get damaged and such.
Sticky-taping to a non-adhesive floppy-plastic sheet wight not work, the negs will sag in the middle when I upturn it.
Taping to a huge sheet of glass would be perfect but fragile.
Taping to a sheet of perspex might work, but wouldn't the light refract weirdly?
All of those methods I envisage the 'holder' will interfere with the light (even though it'll be enlargerlight->holder->negatives->paper) to some degree.

Are there any better ways of holding the negs down properly? How did you go about it?