Preserving ToS over the duration of a download

It seems like a rule like this should work, but it turns out that the initial file that you get when requesting the WMV file is an HTML file which then loads the actual WMV file. As far as I can tell, the request for the actual file does not contain any distinguishing features in the header which would allow you to filter on it. Could you suggest any ways to work around this problem? We don't have packet level control over the application generating this traffic.