Custom Group Membership Type enum

Hello,

     We are trying to implement custom group membership roles. We need 5 roles but the GroupMembershipType has 3 options (Owner, Manager, and Member) for active group users, None and PendingMember don't really count. We have tried using roles but we need for the user role to only apply within a specific group and not across groups. Meaning a user could be a member in one group but  have some other custom membership type in another group. Is there a way to expand the GroupMembershipType enum or some other way to implement what we want to do?

Thanks,

Jean