Shawn,
You can prepare a band of wax and then ask to him/her to press the finger onto the wax. The wax will retain the print. Then you can turn it into a ring and cast it as usual.
Hope this helps a bit.
Leonardo
Easy job for someone who does CAD/CAM work. They can scan the fingerprint and import it into the CAD software and turn the lines into surfaces, booleen those lines from the ring leaving the fingerprint on the surface of the ring...and then mill and cast it. They can even place it on the inside of the ring, but you would have to print that on a 3D printer.