If I were you, I would first keep the scrollbar on "auto",
but make it invisible. Add an event listener that listens for if
the scroll bar is there. If the scroll bar is there, call a
recursive function that adds a certain height and rechecks to see
if the scroll bar is still there. Have the function return once the
scroll bar is no longer there.
I am not sure of the code involved for that, but I think I
would approach it that way.