Set up areas around the server that aren't on main routes that a necromancer can use to store pre-prepared undead with the Release Undead tool and retake possession of them at a later time. This both gives necromancy more oomph and gives those who are undead hunters a way to be proactive about hunting the undead by locating these reservoir areas and hunting the undead stored within them. If balance is a concern, the number and types of undead can be limited based on the potency of the reservoirs.
Maybe make them non-persistent "mini lairs" using the lair system, where a necromancer can app for the ability to make the 'tunnel' that leads to one.
We can use instancing and clever use of separated sub-areas to prevent overlap in the case of multiple necromancers (unlikely)
But this way a necromancer could be coy about where they place these, and undead hunters would have to actively look for them rather than just "oh hey lets go check the boneyard for a necromancer"
I personally think the EE'ing issue makes necromancers much less viable </3