He developed his 'bum-diddy' sound without resorting to the usual frailing style. His right hand movement is an up stroke with the index finger then an index finger downward stroke on the back of the nail followed by a thumb stroke.

I've never seen him use fingerpicks or found anyone who could adapt Seeger style to work with picks.

On "The Goofing Off Suite" he sometimes used a three finger technique closer to his guitar style.