Use categories/manufacturers/features to create secondary site navigation?

[blu_cat]

Hi - I need help deciding how to use categories, manufacturer or features info for this problem:

I want a left block that lets users display products by 2 categories - categoryA and categoryB - where categoryB data is a subset of categoryA. (Like Honda > Accord, see attached)

The site is selling car parts, so I need to include compatibility info for categoryA and categoryB for each product. Each product will have a single value for categoryA and multiple values for categoryB.

BUT I don't categoryB to appear in any of the site's main navigation - only in the site's special left block. I also need categoryB values to be searchable by the user - products tagged with categoryB need to show up upon search.

How can I use categories, manufacturer and features to do this? Do I need a custom module?

[blu_cat]

I can set up categoryA as Manufacturers, but then categoryB would need to be a subcategory to the Manufacturer block data. Is this possible to do?

Or, I can use Categories and hide navigation for categoryB, but then the categoryB values do not yield any products through the site search.

I'm stumped - any help would be so much appreciated!