In OBIEE 11g dashboard prompts there is an option called "Require User Input". If you will enable it then it will force user to select some values in prompt and then only user can see "Apply" button. In reports when you will say is prompted for that particular column then instead of making it as " is prompted" make it null.so when we you select some values and say apply that time only user can see data on reports.
If I understand this properly, your problem is that you never want a user to create an ad-hoc report containing "supplier name" that doesn't also contain "supplier country". Is that correct?
If so, couple of things you could try.
1. Combine supplier country + supplier name into a single field like "USA - Supplier #1", so that users have no ability to not select the country