Internet Explorer unable to download Excel files over HTTPS

CSV downloads work fine over HTTPS in IE, however Excel downloads give a strange error:

"Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later."

According to Microsoft this is "by design" http://support.microsoft.com/kb/316431 (insert eye roll here)

I found a similar issue and patch here: http://drupal.org/node/749812#comment-3342500 and adapted the patch for this module. In my testing the Pragma header was not required. Patch against 6.x-2.x-dev attached.