When there is but one shift key, use the fourth finger of the left hand on the shift key. This will make it necessary to change the fingering somewhat for the capitals on the left hand side of the keyboard.
Hold the shift key down with the fourth finger, and strike the letter with one of the other three fingers, as most convenient.
The shift keys at present in use are awkward, and it is a matter of surprise that no manufacturer has yet brought out a shift key which can be used with the thumb which now has nothing to do; in this way there would be no change whatever in the fingering.
Manual of Dougherty's brief shorthand and touch ... . - Full View | HathiTrust Digital Library:
shift-key by each thumbs or center shift
shift-key by each thumbs