Yes, you can contact print them onto a slow ASA film (although your emulsion will be reversed in the mount, so they may not focus properly if mixed with normal camera-exposed slides).

A second alternative may be able to illuminate the negative from behind with a light box and shoot it directly with a macro lens.

The third alternative, of course, would be to make prints, shoot them, and reverse processing the film. I have done this in the past when a customer wanted some old prints made into slides to project at a party or special event.

Unless you have a dedicated medium format projector, the latter alternatives also offer the flexibility of being able to reduce the medium format frame either to a 4x4 (127 "Superslide") frame or a regular 35mm frame. Either will then project using a conventional Carousel type projector. (The 4x4 frame mounts are getting hard to find but still pop up on ebay from time to time).

Ed