Hi Clarissa!
I have ran into the same situation as you and Philip, but I prefer the way “Do More” goals work in Beeminder over “Do Less” goals, so I usually set up a “habit” goal and a “habit days” goal. That way both are “do more”. It can be completely automatic if you get a premium plan that supports custom goals, and then setup IFTTT.
I wrote a bit about it here: Nifty trick for "days I did this other goal" goals