CiviMail click-throughs not tracked with checksum token

It appears that when using the

{contact.checksum}

token in a URL, CiviCRM is not tracking click-throughs for the CiviMail report.

Trackable links currently use a redirect via /civicrm/extern/url.php?u=XX&qid=XXXX . A proposed solution would first add in the redirect url for a link that contains a checksum token, then modify the url.php script to accept another GET variable that contains url-encoded variables from the external link.

For example:

http://mysite.com/donate?cid=3&cs=ef2fdef1ac85b27a8b77a2edf57c0c7f_1301503387_168

would be turned into an external link such as:

/civicrm/extern/url.php?u=XX&gid=XXXX&vars=cid%3D3%26cs%3Def2fdef1ac85b27a8b77a2edf57c0c7f_1301503387_168

which allows the $_GET['vars'] value to be decoded and attached to the registered external URL.