I've scanned negatives both larger and smaller than the usual 35mm that my scanner has a light for (Which never worked! ) By placing a lightbox on top of them and scanning. The light box is a simple thing used in sewing and art to help trace patterns. Not all that expensive either.
This one is like what my wife has.
http://www.joann.com/light-tracer-li...n/4128500.html
This one is small and inexpensive, but they say "bulb" for the light which makes me think it may be a regular one. That might generate too much heat for nitrate.
http://www.google.com/shopping/produ...FngaAr7I8P8HAQ
Steve B