The man who made my Celtic lever harp, using plans from Markwood in the U.S., also made a lot of other stringed instruments and he played a mountain dulcimer which he had made. He was a carpenter by trade and lost the top of a couple of his fingers in a work accident, but he played the dulcimer beautifully. I think, from memory, he may have sometimes used a block like a barre, moving it up and down the strings or maybe that was someone else I saw playing one. He passed away about 20 years ago so it has been a while since I saw him playing.

A lap guitar with the barre device might also be worth checking out.

The other thread is here:

Guitar: Rock-it barre device. Anybody tr[y it?]