It turns out that I was a little bit fast in verifying the result last time. The usergroup promotion is not working as expected (probably because I'm doing something wrong).Do it the easy way.
Create a usergroup promotion with some arbitrary criteria such as "User State Is: Valid" that promotes them to the desired usergroup.
That would effectively make everybody a member of the usergroup. unless they are awaiting approval. In which case, as soon as they are approved or have confirmed their e-mail they will get automatically promoted anyway.
There's a code edit to get around that. Would be good to make that code change now to get done what you need to, then revert it back to normal.Note that the cron only updates users who have been active in the last 72 hours, so there may be a delay for some users despite manually running the cron.