Sure, I understand where you're coming from. I still think there's no easy solution to this, but maybe someone else will have some interesting suggestions.

What I was suggesting in my first reply above is pretty much in line with what Baptiste is saying below. Google used to be very tough on people trying to index search results pages and that's why personally I would try going a bit different way.

Cheers!

Technically, the search engines don't want to crawl other "search results". Personally I would try to get individual pages and category pages indexed, while avoid trying to index and "canonicalize" search result pages.