Nifty! That’s a clever idea.
I believe you could do it with just Tasker if you want to. You can use Tasker to submit a data point directly to Beeminder, using either the Plugin > Beeminder action (if you have the Beeminder app installed) or with a direct POST to your goal using Beeminder’s API.
I find the latter more reliable, possibly because of a bad internet connection here. I was finding that sending data points failed far too often for comfort using both methods (from timeouts IIRC), but for the latter method my Task can easily check the response code and if it’s not a success I can repeat the attempt. Using the Beeminder app plugin though is super-easy and available as soon as the Beeminder app is installed. You may want to start with that and stick with it if it’s always successful.
In case it helps though, there’s some info at Help adding a datapoint from Tasker using Beeminder API about using the Beeminder API with Tasker (and probably in a bunch of other places too; that was just the first one I found), but you’d be welcome to post here if you had questions about it or needed help!