So I just want to make sure I understand what you are looking for here...You want to make a temp redirect to a new homepage that will, realistically, only exist for a little while, few hours tops, and you don't want it indexed. I am imagining that this new HP is going to live on the same domain?
If so why don't you do a 302/JS/Meta Redirect to the new HP and then also adjust the robots.txt file to disallow that from being indexed and to be SUPER SAFE you could rel=canonical the new page to the old page.
Does that help?
