Not sure about the benefit of starting up a brand new site just for Yahoo, you risk a duplicate content penalty in Google if you do it. Unless of course you don’t plan on having any links pointing to the new page (how Google will find you), in which case you won’t rank anywhere on Yahoo anyway.
As for the sandbox, you can have your entire site indexed by Google, be a PR7 and spidered a few times every day and still be in the sandbox. The sandbox is just a filter that is triggered that doesn’t allow your site to rank well for highly competitive search terms. In the scenario I just described, you would rank very well for non-competitive terms.