Add Group-Off or Group-On buttons

“control: hidden” is the only way to turn off a group switch. However, sometimes I want a group which only has an “off” button. (For instance, turning all the lawn sprinklers off with one click makes sense. On, not so much.)

I know that I can manually add a separate button to the group, but that takes up space and requires additional programming, so “control: on” (plus maybe a “control-icon” field?) would be great.