.htaccess run XML file as PHP

So I have a page http://ift.tt/WfcuFI

I want to make it so that if I go to http://ift.tt/1v1Y1YC, it will be treated like the above URL.

I placed:

RewriteRule ^sitemap.xml$ sitemap.php [L]

in my .htaccess file but nothing is happening.