Customer-specific Ideas Portal (or portals with applied filters)

I would like to be able create an Ideas Portal for a specific customer or set of customers (e.g. Beta Testers).  This portal would need additional filtering options, such that only Ideas which meet the filter criteria are displayed.  Example criteria would include:

• portal users (e.g. only show Ideas created by a portal user)
• custom field (we have a field for customer name)

This may also require the ability to filter Ideas in the other portals.

As a specific use case, I want to give Customer X (with 5 named portal users) access to a portal where they can see their submitted ideas, including "customer impact" and the name of their colleague who submitted the idea.  However, I do not want these Ideas (submitted by Customer X) displayed in my general customer Ideas Portal.

I can get part-way to what I need with the partner portal settings, but it only works for one customer.  If I have a second customer where I want to provide this capability, they each would see each other's ideas.