Simulating Level 4 Scroll with Subpage Problems

Requirement: Display a 4th level of scroll results (Date -> Purchase Order Line -> Purchase Order Shipment Line -> ** Purchase Order Distribution **)

My plan was to create a sub-page for this, adding the fields from the parent (which show up on the subpage as level 0 but is really level 3) and then add a grid for the rows (which shows up as level 1, but is really level 4), then manually populate the scroll. However, when I do so, it fails to save with "Incorrect Scroll Level"). I can't make the grid a level 0 grid on the page (it doesn't let me change that).