Off the top of my head:
- Remove them from Developers (they are added by default.. ha ha, be quick!)
- Create a new group for that project.
- Add them (and anyone else!) to that group.
- Go into the repo user permissions in the client (I think this changed with the new GUI)
- Add that group to the project repo
- Make the permissions match Developer
I believe that's all of the steps. I should really make a quick guide or something for this...