One problem with loss of sensation when holding the fly, especially when the fly is small. Tying the knot is mainly visual.

Have your friend get an E-Z Hackle Pliers to hold the fly by the bend of the hook. It then is easier to rotate the fly for a clinch knot. The hackle plier can be clipped to the string on of a zinnger so it can be removed when it is needed. You can put the open end ring of the hackle plier around the tip of a finger to make it easier to hold and spin.

It's worth a try.