What sort of feel/tempo do you need?
You could hook your guitar up to a reverb unit/ a delay unit/ a tremelo, come up with some neat chord progressions and improvise over them. The purpose of the effects would be to substitute for a rhythm section and put your improvisations in context.
Some suggestions:
1. Ry cooder got a lot of instrumental pieces. The "Paris, texas" soundtrack is a collection of really slow ambient stuff. Maybe a little too slow for a wedding.
2. You could take tunes like you "I just called", thump out a bass line (or note) and
slide the melody over it. Its still gonna be a little slow though.
Azrael.