Internal users as customers on other service projects

[Rowell]

We both have Service Projects, Business and Software types within our JSM and we limit the access on product level which means that Business and Software users don't have access to Service Projects and vice versa.

For some reasons, we have to open 1 Service project to Business and Software users for them to raise their inquiries internally BUT as customers not as agents, meaning Customer Portal access only.

Service Project users will remain no access to any Business and Software project types.

How can I set this up?