Adding variable to URL is deleted after saving post

To get video to display properly inside video.php (attachment template) I want to add the native width and height to the link to the attachment, but that information is stripped right away by WP after saving the post. How can I prevent this from happening, or is there an easier way to display videos (flv’s) in different sizes?

<a href="http://www.domain.com/?attachment_id=8723&width=512&height=288" rel="attachment wp-att-8723">Linkname</a>