Here's what I would do.

1. Get a peice of glass and a piece of wood or matt board or heavy card, both cut to the the size of the paper
2. Lay glass face down
3. Mask off the areas of the glass around the negatives with black tape (choose something thinner than the negatives)
4. Place negatives onto glass
5. Place paper on top
6. Place board on top of that
7. Sandwich the whole thing with 5-6 of the large binder clips from the office supply store