Just figured out how to get around the limitation with Beeminder’s integration! Put simply, don’t use Beeminder’s integration at all. Use the HTTP Request action to post to Beeminder’s API directly instead:
Note that I’m using two custom global variables, %BmUser and %BmToken, to store my username and API token. You’ll need to look up your API token and store it and your username in a couple of variables you create if you want to take the same approach.
%TIMES is a standard variable that Tasker defines as the current time in seconds since January, 1970, which happens to be what Beeminder expects in a datapoint’s timestamp field.
Using this approach you can send any Tasker variable you like to your Beeminder goal as the value for a new datapoint.