Don't know if this is much use to those who make their own blocks, but when you posted this, it did occur to me as a block modification technique.
Suppose you have a thin based waterblock, (Say a Maze2) and you want to give the bottom of the water channel some texture to increase surface area and turbulence.
Instead of taking a tool to it and reducing the base thickness, you could mask off most of the channel, except for dots along the bottom, and plate up little copper posts.
I'm not sure how cost effective it would be, but it certainly could be done.