After weeks of failed attempts, I've finally found the means of creating autonomous zombies en masse that do not require a constant effort from the necromancer.
Unfortunately, most of these creatures are blindingly stupid and docile. They'll defend themselves when threatened, but are otherwise content to bumble about aimlessly. Luckily a few zombies per batch seem to be naturally aggressive. When this aggressive variety is placed within the docile group, it acts as a sort of guard dog, alerting the others to prey. I've not yet figured out the trick to producing this useful variety consistently, but the ones we have allow some degree of control over the entire group.
And that's enough for the Pellingares.