With the little I know from him, like most of us Howard developed his own technique for playing the theremin.
I agree he's got an amazing sound and his playing always has a great sense of feeling.
Howard Mossman is one of the longest standing members of the theremin community.
There's an old picture of him playing his RCA on the picture archive page here, srcoll down to "September 2001 - Howard "Uncle Howie" Mossman" on 2001-2002 Picture of the Month Archive (http://www.thereminworld.com/gal-pom-2k.asp)