Custom mime types for respond_to


Is there a way to add a mime type of my own to respond_to ?

There’s html, xml, js, ical etc …

But I want to be able to respond_to Excel.

Excel has the following content-type header:

I want to use the new ?format=xml querystring parameters that respond_to
can respond to.

So I want to pass in ?format=xsl or ?format=ms-excel so that I can
return my results formatted for Excel.

Any ideas? Or do I need to potter around in the mime_type.rb source