An idea that I have been tossing around in my head for a while is a one shot magic item called the Bones of the Horde.
Each bone radiates a faint aura of necromantic magic. When exposed to positive planar energy, such as from a turning attempt, each bone turns into a normal undead skeleton. This effect uses up 1/2 hit die worth of turning effect. After a short period of time(10 rounds) the skeletons collapes back into their single bone form. Of course if too much energy is directed at a bone, it will turn into a skeleton which is promptly blasted into oblivion.
Just equip a room with several piles of bones in different areas, and watch as a small handfull of skeleton triples in size when the cleric turns them once. Of course, a second turning would wipe them out, but the cleric might be a little leery of trying to do so.