I posted this mod (written by me) to donnoman's plugin 2 months ago on the CPG-Contrib board. Now I post it here as well for good measure.
If an admin prefers not to have it here, feel free to remove it.
This mod summarizes the stats for categories with sub-categories. Read the README.txt file for more information. There are config settings at the beginning of codebase.php. You need to set them in that file. There is no config panel right now. Please do not discuss this mod here. Head over to the CPG-Contrib board for CPGOcat to discuss this mod or anything else having to do with this plugin.
Here's the relevant thread where this mod was proposed: http://forum.coppermine-gallery.net/index.php?topic=27460.0