The answer is you can't have direct table access to linked data dictionary tables, only SQL access is allowed.
However, you can imitate direct table access by using views that SELECT * from the table you wish to access.
Table CUST is on Data Dictionary B(with a linked name of link), but you want to "direct" access to table CUST from Data Dictionary A. So on Data Dictionary A, you would create a view called LinkView_1(this can be called anything) and define it as "SELECT * FROM link.CUST". You could then from your application connect to Data Dictionary A and directly access view LinkView_1 as you would any table.
Please note that both Data Dictionaries must be on the same server.
Since you are using a view, you are going to be dealing with an SQL Cursor. Only a view that creates a dynamic cursor will post updates back to the linked table while a static cursor will not. For more information about Dynamic vs Static cursors, please refer to the help file.