Django，按模型外键按组过滤用户

I have a model for a blog post where the owner of the post is a foreign key to User. With that model any user can own a blog post. I would like to change it so that only the users in a certain group -let's call it 'bloggers'- can own a blog post object. Ideally it should appear in the admin too, I mean in the blog post admin right now the menu for 'owner' lists all the users, it should only list the ones in the 'bloggers' group. How do I do that with Django 1.3?I have a model for a blog post where the owner