What is the universe like? Does it have both tables in it? If so, you might be able to do something with Table Mapping – but you’d have to be able to reopen the query panel (in the tool that created the report) with a userid that has been set up in Supervisor to have the tables “swapped”, if you will, via Table Mapping – to generate different SQL.
Or am I totally misreading your question due to too little information?
Is this really for WebI 1.x/2.x (which corresponds to BusinessObjects versions 4.x/5.x) – or is this an XI issue?