Cannot add a user to project as an Owner (even if they created the project)

Scenario:

• I have a group with several projects in it.
• I am the owner of the group.
• There are many other developers in the group, either Master or Developer role.
• A user that is Master role in the group needs to be Owner role on one of the projects

I've tried going to Project > Settings > Members > Add Member however the only options for the user role is Guest, Reporter, Developer, Master but Owner is not listed in the drop down.

I can add the user to the entire group as an owner, but this is not at all the goal, this user should not have owner rights across the entire group of projects.

How can I add a user as an owner role on a project, but not the entire group of projects?