Uncle Jacque, this may be what you're looking for (or close to it).

In 1961, I had a chance to buy a genuine flamenco guitar from one of the top luthiers in Madrid. He was sufficiently back-ordered that it took a year and a half before he sent me the guitar (which more than exceeded my wildest dreams!), and he included the customary çejilla (pronounced "Say-HEE-yah"—means "little eyebrow," from the curved shape), which is standard equipment with a flamenco guitar.

Here's a picture, with some history:   CLICKY.

Not very many music stores in the U. S. have them, or even know what they are, but I managed to acquire a couple of them, one for each of my nylon-string guitars. Or if you're handy with simple tools, it wouldn't be that hard to make one. After seeing mine, a friend of mine made one for himself. Or you should be able to buy them on-line. Just google "cejilla."

By the way, the string you wrap around the neck of the guitar is just an piece of a used G-string (save one when you change strings). It's a good idea to glue a strip of leather or felt to the bottom of the çejilla long enough to wrap around the back of the guitar neck so that it sits between the neck and the length of string. The bare string can mar the finish of the neck over time.

These things work like a charm and are about the perfect capo for a nylon-string guitar.

Don Firth