Zenobase seems to work with Google Fit (and Zenobase can publish to Beeminder).
I created a dummy Beeminder goal with a very small slope to test it. Just had to link Zenobase to Google Fit and to Beeminder, and then in my Zenobase Fit bucket add a task of type beeminder, goal = nameofmygoal, values = count, left filter blank (later you can e.g., filter out steps that occurred in a moving vehicle), timestamp blank, and then you can choose what day to start from.
This is still kind of rough–I’m looking at how closely the Fit API data correlates with the number on Google Fit on the phone (the latter is the most stable/accurate one I’ve found so far on my phone, without going to a separate pedometer), but I thought I’d throw this out there. Note that on the free Zenobase account type, you have to press a button to sync your data.