Depends on the ability counter. Some of the icons are not centered on the punch out (like the Deathtouch one here) so it may not line up perfectly. A custom printed one would work well though!

As for size, sandwiching one between 2 bumpers would work well. The tops are flat, so there would be no worrying about it rolling. Size-wise, a double stack comparable to the Chessex mini d6's