I think by "bimanist" Shade means simply that he holds his Gillette razor with both hands while shaving. I remember those "double-edge" razors, and they were not what is now called "ergonomically friendly."
In reading these recent posts, I was reminded of The Prisoner of Zenda as a possible source of Kinbote's fantasies. Checking on this, I came across this exchange from five years ago:
http://www.libraries.psu.edu/nabokov/hornboyd.htm
All private editorial communications, without
exception, are
read by both co-editors.