excel

I am using betwixt and domify.  I want to reuse the same controller to either output html (which I already do) and excel.
 
I added another command which uses a different xsl to format for comma separated value.  But, the output method is text so it just shows as text in the browser.  How do I change the content type so the browser things the response is application/vnd.ms-excel?
 
Thanks,
Paul