Firmly clamp battens the same thickness as the door to the bottom of
the door, flush with the original end of the door

Of course, I didn't mean to the bottom of the door, I meant clamped to the
sides of the door, set flush to the bottom.

i.e.

| |
| |
| Door |
| |
+| |+
|| || -- Batten
|| ||
++-------++

This way, the batten gets splintered at the end rather than the door.
Obviously a skilled craftsman will be able to use the plane directly, which
is why I use the battens.

Christian.