Design Question: Keys using multiple Databases

We are a team who is developing database applications with Informix-Online 7.23. We are looking for Informix-Developers with experience in Informix who help us to find a solution for our problem. We are designing multiple databases. We intend to design a database with general (static) tables, that are used from several of our applications. Beside this database, each application owns one private. The tables in the private databases have associations with tables in the general database. This would mean that we need foreign-keys that span two databases: The primary key of tables in the general database should be a foreign key for tables in the private database. We would appreciate any idea how we can implement this concept without loosing the primary/foreign-key relationship. Thank you, Jens