Keep in mind 1 size down = 1cm smaller boot sole length (in same brand)
(with the exception in of the Lange Exclusive series in a 24 and
24.5). There are many bindings out there that can adjust to
accommodate this.
Also padding certain areas like the heel and the shin, do not make a
boot smaller, they are mainly used in realigning the leg in the boot.
Heel lifts can be used if the ankle area has too much height, but it
really does not make the boot smaller. your foot is still going to have
too much room around the foot. Goes the same for L and C pads around
the heel bone.
As rob said, adding padding to make a boot fit smaller is not very effective, usually ends up being pretty painful, and takes a long time and is thus very expensive.