Off-Site Amazon Affiliate Links

For those who host Amazon affiliate links off of their approved domain, how are you cloaking your traffic to make it appear that it's actually coming from one of your approved sites?

I'm running WordPress as a CMS if anyone knows of a proper plugin. Thanks!

Would using a URL shortener from Google help?

No, unfortunately Amazon prohibits that. I believe they track referring URLs to ensure content comes from the "approved sites"