[Toadling]

I don't think there's currently a way to do this. The best you can do is save a review perspective with the undesired groupings collapsed, leaving only the "Review Today" group open. That's what I do and I've been satisfied with it.

As an aside, the Omni Group mentioned a while back that they were considering adding smart folders. Maybe that feature would allow you more flexibility in what is (and is not) displayed in your perspectives. It might also provide a solution for the people yearning for a "due today or flagged items" perspective.

-Dennis