How to open XML File from IE into an external app?

[J Wilks]

I am trying to download an XML file via Internet Explorer and view it in an
external application. The file has a KML extension, which is registered in
Windows file types to my external viewer. So I type the following into the
browser:

http://localhost/test/myfile.kml

And IE displays the XML, instead of launching it in my external viewer!

I can get around this by having the web server drop a
"content-disposition=attachment; filename=myfile.kml" in the header, but I
need it to open by default every time, and apparently auto-opening files is
not allowed when a content-disposition header is set!

Anyone know a workaround? How can I open this KML file in my external
viewer, without IE snooping it, learning that it's an XML file, and then
opening it up itself?