Is there anyway to add the HTTP Referer to the URL of a custom Umbraco 404 page? This is useful for finding out the page the visitor requested that caused the 404 error. It's also really useful in Google Analytics tracking for this reason, too.

Basically, what I'd like is the URL to contain the refferer. So, imagine a visitor types in:

http://www.mysite.com/donkeys.aspx

However, the "donkeys" page has been deleted so they get redirected to my custom error page called NotFound:

http://www.mysite.com/notfound.aspx

What I'd like is for the "notfound.aspx" page to add in the referering URL as part of the query string like this:

http://www.mysite.com/notfound.aspx?referer=http%3A%2F%2Fwww.mysite.com%2Fdonkeys.aspx

Is this possible in Umbraco? Whenever I try and access HttpContext.Current.Request.UrlReferrer in an error page I get nothing. Same goes for document.referrer in javascript.