Bottom line - all the smart people here couldnt find a way to do it? Maybe what I suggested wont work (I'd be happy to here technically why not and not just "google almighty will kick your ass" kind of answer) but maybe some variation of it will?
google obtains whois information based on domain/ip
google obtains information on other sites on same ip.
google spiders the content based on domain/ip
google provides ads based on content at domain/ip using javascript.
google provides other services (adsense, adwords, gmail etc) using javascript
javascript has a number of built in objects which provide the browsers environmental variables which google collects
google then uses all that information to "understand" customer behaviour for all its services by analysing patterns (same server ip, same client ip across multiple logins, same whois details, same nameservers, same mailing addresses etc).
so, unless you been a ninja from the start across anything you have been doing with google then chances are it is simply not worth the effort to bother now.