adamcrouchley,
Unfortunately, what you’re asking for just isn’t currently possible. However, the Community Submission form will honor your ‘Default Content’ settings (Events->Settings->Default Content), so if you select an existing Default Organizer, then Community will honor that. If this is something you’d like to see in a future release, I would suggest submitting it as an idea on our UserVoice page. Our team periodically reviews the most popular ideas for possible inclusion in a future release of the plugin.
I know that’s not exactly the response you’re looking for, but hopefully that helps to answer your questions. Just let me know if I can help further. Thanks! 🙂
-Casey-