How can a user with read-only access to Git make a pull request?

How can a user with read-only access to Git make a pull request?

I'm working on some collaborative projects with my coworkers. We're
starting to adopt Git.
I have a repository in Bitbucket, and I gave read-only access to one of my
associates. After he made ​​his corrections and contributions
to the project, how can he make a "pull request" if his user profile is
read-only? How can he upload his branches to the repository?
The second, taking a user profile writing, as we can prevent its branches
merge repository to master without having gone through a "pull request"
and that the administrator has decided to accept your request.