You can install the Gemini CLI (https://github.com/google-gemini/gemini-cli) but assign a "paid" API key to it (unless you pay for Gemini Ultra).
But this is if you want to pay per token. Otherwise you should just be able to use your Gemini Pro subscription (it doesn't need Ultra). Subscriptions are at https://gemini.google/subscriptions/
Is that correct? I can't even upgrade a Group separately?