1st suggestion:
To have a special monster army with special abilities. You can have a hamlet, city, metropolis etc. filled with at least one creature type OTHER than humanoids and this idea promotes the concept of Geb's citizens and rulers. The soldiers can have the normal stat block of the creature but with a few exceptions:
1- It's Combat Rating can not go above the normal point/tier progression (example: Geb can have Skeleton trolls (which naturally belong to the combat attribute). They are normally Combat Rating 6, but because they belong to the combat attribute, they have limits. lets say that Gib has
1 point in the Combat Line and it current tier is also one; thus the troll skeleton MUST follow the basics below:
Tier 1: Private (change to troll skeleton), a CR 2, HD3 undead warrior2/Expert1.
So, if you really want a troll skeleton to guard your kingdom, you must change the troll skeleton's stat block accordingly, which may take vast amounts of time.
And also, since trolls naturally have regeneration, we can simply keep the special ability but at a cost. and unfortunately, I still don't have the basics for the 'cost'. Suggestions would be of great assistance. How I imagine this, is like an Eidolin's point buy Evolution which utilities points to make the creature stronger in different respects.
TO DMs, they can add special classes or prestige classes to the skeletons for extra fluff or for specific powers, according to the monster's creature type (which is undead).
I hope this helps with the process.