I want to use some of project features, so I have modified the project form, and created a new menuitem for it, with some domains and context, and a new group for the security.

My problem is that i want to create a new security  group. That group will inherit the security from the group Project User, but i don't wan't to show the Project Main Menu to my new group and I don't want to hide it to the users that already belong to the Project User group. 

Is there a way to make this without creating a new group only for the project menu item?