How can SOLR be made to boost within result set?

Question

I have indexed some documents that have title, content and keyword (multi-value).

I want to search on title and content, and then, within these results boost by keyword.

I have set up my qf as such:

  <str name="qf">
    content^0.5 title^1.0
  </str>

And my bq as such:

<str name="bq">keyword:(*.*)^1.0</str>

But I'm fairly sure that this is boosting on all keywords (not just ones matching my search term)

Does anyone know how to achieve what I want (I'm using the DisMax query request handler btw.)