Restricting access to a logon page

I've got an access policy with two logon pages. The first is the landing page and it has a single textbox on it where a user enters their account number. I want to keep the user from getting to the logon page until they've entered their account number. It works just fine right now, but if you refresh your browser on the landing page, it takes you to the logon page. Is there a way that I can prevent that?

Thanks!