Can Apache Solr Search allow a user to search 'within' current results?
This is from my experience using Database Search not Solr but it might work. 

I'm also not sure it's exactly what you're looking for but it might be a starting point.


Clone your view, but keep the URL the same.


This allows you to run two exposed forms both of which re-direct to the same view. So I have one on my homepage and then one on my search results page. When you search from the home page the values are automatically populated into the second exposed form when you land on the results page.

Because the exposed forms are different this means you can show more fields on the exposed form on the search results page and because it remembers the first search, technically, you're searching within the original search.