When the user clicks on a portal row in the Projects portal, you'll want to set a global field to the primary key field of the project. You probably have a relationship already between that primary key and the corresponding foreign key in Project Items; now you need one from the global to the foreign. Your second portal, the project items, should be based on this new relationship. When the field is set, and committed, the relationship resolves.
My personal caveat is that I haven't used Go, but see no reason why this would be different than the desktop with regards to this.
I got it... Thanks!