Login on top of every page?

[eluser]Unknown[/eluser]
Hi guys
I'm building a site in CI for the first time and have stumbled on to some trouble.

Basically, the site has products like this:
http://www.mysite.com/products/foo
http://www.mysite.com/products/bar

I've created a MY_controller that all the other controllers extend so I am able to make a login system. What I don't understand is how I can make it so that the user can login on every page so when they click on "Login" the same page is loaded but with a form planted on top, e.g:
http://www.mysite.com/products/foo/login

My plan is to use Ajax for this, but as I want the site to degrade gracefully for non-JS-users I'd like to create this approach first. Another alternative would be to have a login-controller that after the login redirects the user to the page where he / she was (pretty much like the one here on the forum), but I'd prefer the first variant.

Any pointers or tips?

Cheers
Stefan