The thing is it wont really work on a chromatic autoharp but might with an autoharp tuned diaronically? Alternatively, try playing your autoharp with teaspoons for a nice autoharp effectt that will make it sound like a dulcimer! Look on youtube. You can also play with thimbles as stoneman did for a nice zithery effect. In the same way as prepared piano, you might try laying found obljects on the strings such as paper clips or morris bells or coins for some new age playing.

Pat