If Yahoo is offering this service, then I'd say no, you can't do that. More importantly, I'd say you SHOULDN'T do that. If you have the "wrong" URL in the address bar, it causes a couple of problems. First of all, if the user decides to make that page a home page, or copy the URL to direct someone else to that site, it won't work. Second, if the user refreshes the page, it will refresh back to the home page, rather than just refresh the page they were on. This is VERY frustrating, and when this happens to me, I usually just leave the site.
There is nothing wrong with showing the address the user is on. Unless you have a very compelling reason to mislead them, I would leave it alone.