The “solution” I came up with was simply to use the cursor positioning feature to write to the lines I wanted. Since you’re writing strings anyway, it’s not terribly difficult to do. If you’re making a display for a project, just account for what ends up on what line.
I can’t help you if you need upward-scrolling text. You could try to modify the liquidcrystal library to handle it all on the arduino, but that seems like more effort than it’s worth.