Redirect plugin for multisite

I sometimes use redirects for marketing purposes to help track how a particular advertisement performs. Instead of buying and using new domains, I’ll redirect an unused subdirectory to our landing page with a tracking extension appended to the end of the URL.

For example I might create a print ad with the url as http://www.mysite.com/vanityurl

So I can track the response from this ad, I would like this url to redirect to the correct landing page but include a Google tracking extension appended to the URL.

Landing Page URL: http://www.mysite.com/landing-page

Landing Page URL with tracking extension: http://www.mysite.com/landing-page?utm_source=time-magazine&utm_medium=print&utm_campaign=product-name

I’m currently researching how I can accomplish this easily on WordPress multisite as I don’t want to redirect every domain’s subdirectory on my multisite network to the same landing page.

Does anyone have any ideas on the best way to accomplish this?

I found this but it didn’t work correctly for me: http://www.ninjaxservice.com/blogger-tips/how-to-setup-wordpress-multisite-301-redirects-for-multiple-sites/

Thanks!