I usually do both shifts together for Caps Lock. I basically never use it anyway.

In my case, I have a physical Escape key, but use Caps as my "hyper" key to interact with the WM.

If you're using X11, the incantation goes into your keyboard config (the last one is what's of interest):

    % cat /etc/X11/xorg.conf.d/90-custom-kbd.conf
    Section "InputClass"
      Identifier "keyboard defaults"
      MatchIsKeyboard "on"

      Option  "XKbModel" "pc105"
      Option  "XKbLayout" "us"
      Option  "XKbVariant" "mac"

      Option  "XKbOptions" "shift:both_capslock"
    EndSection