If you look at my WY-30 pictures, "capslock" (next to spacebar, as God intended)) is the same size as enter (2X). CTRL (next to "a" in QWERTY and Dvorak) is slightly smaller, and a much better choice.
I have blank modifiers on my unicomp, and it both looks sharp, and is useful. Have you considered checking out if WASD or SP have the right length and profiles?