Continue drawing to the normal mode buffer, but when the list is scrolled blit the already rotated window contents (area A) to the new position, update the normal mode buffer with the changes, extract the exposed area (area B), rotate it and copy into the window.

When the list is scrolled up the exposed area is at the bottom so area A is the bottom of the list minus the top portion that gets moved off screen and area B is the new contents at bottom of list.

That should improve scrolling speed since you are only drawing and rotating the newly exposed area. The rest is blitted from its already rotated form.