We ran into a similar issue: We needed to retrieve data from several tables using a stored procedure. But the business object we based the call to the Sp on would only show us the fields in the table that busienss object was created for.

Our solution: Create a view in the database that contains the four tables we needed to retrieve data from. Then use the business layer generator to create the objects for that view. We had to hand-code the stored procedures, but that wasn't a huge issue. Now we can retrieve and update data to these four joined tables.
Lynn 8-)