The author of the Askapache blog has a great writeup on how to create an “MCC” (My client center) account for Google Analytics.The 10min install let’s you create an autologin for your clients (or your own sites). Here the short form on how it works:
1. Create a Google Analytics Admin account
2. Add a non-admin account for each of your client
3. Place a specific code for the button and the form. Full specs here.