I just had a Homer Simpson moment when I realized that Google provides the following simple tool for building URLs that track custom variables in ad campaigns and I had not known about it until today. Check it out here.

You can enter the variables you want to track in an online form and Google will generate the link with query string in it.  Use that link in your ad and then Google analytics will pick up the traffic from that ad in your Google analytics account. And I’ve been using redirects on my servers all this time.

Doh.