In Solr I can use the query function query to return a numerical score for a query and I can user that in the context of a bf parameter something l
Alternately, if you've got something in that bf that's heavyweight enough you'd rather not run it across the entire set of matches, you could use rescore requests to modify the score of the top N ranked ORIGINAL QUERY results using subsequent scoring passes with your (cat, dog, etc...) scoring-queries.