Since a trackpoint can't possibly support two-finger scroll, which is what makes scrolling both directions so easy on a trackpad, it seems like you either would need to drag the scrollbar block or hold down a key in order to scroll, two cumbersome solutions.
You just hold down the middle key and push the trackpoint. Since its right by your thumb anyways, it really isn't cumbersome at all. And I find it much easier and more precise for scrolling long distances than either trackpad or screen scrolling since I only have to hold something down, and releasing it stops the scrolling instantly.
Since a trackpoint can't possibly support two-finger scroll, which is what makes scrolling both directions so easy on a trackpad, it seems like you either would need to drag the scrollbar block or hold down a key in order to scroll, two cumbersome solutions.