Any way to make new users default to multiple groups?

[Jayfore]

Once I activate a new user, I would like for them to default into more than one group. I use the ezGallery plugin, and after a user has 20 posts, I want them to have permission to upload images to the gallery without requiring approvals... So I thought I would use the Group Promotion feature. The ways that I can see for doing this would be:

1. Find a way to make users default into "Registered" and "ezGallery Not OK", where the latter can upload images, but they require approval. After 20 posts, group changes from "ezGallery Not OK" to "ezGallery OK", which can upload images without requiring approval.
   
2. If defaulting to multiple groups is not possible, can move users from "Registered" to "Registered + ezGallery OK" when they hit 20 posts. No need for a group called "ezGallery Not OK" in this case.
   

Any suggestions would be greatly appreciated. Thank you!

[DrBaja]

I'm not sure how you could do this using myBB features but, a plugin like myBot for myBB 1.8 would work.

Just configure the bot to, on user join put them in this group as an additional group.

MyBot for MyBB 1.8: https://community.mybb.com/mods.php?action=view&pid=1