The linked idea was posted on behalf of my brother
Sturton, and a suggestion from [hippo] inspired this far
superior idea.
To the left (or right) of the trackpad on a MacBook,
there
should be two recesses which can accommodate the rolls
of
a small replaceable paper scroll, perhaps bearing
only a
few feet of paper. A hinged bezel folds down,
concealing
the recessed rollers and framing the paper between
them.
Under trackpad, mouse or key control, the scroll can
travel
backward or forward between its limits.
Gadulka! You now have a space in which to make
doodles,
sketches and other suchlike and, at the swipe of the
trackpad, the scroll can be advanced to reveal fresh
paper,
or rewound to locate old items.
Cunning software, coupled with a position encoder for
one
of the rollers, can even allow you index and retrieve
specified scroll positions.
Even cunnier software would make use of an inbuilt
linear scanner, allowing your sketches to be captured as
image files for further manipulation.