id probably achieve this in this way:
1) lvl 1 psion + Practiced Manifester & Inquisitor Feat, lvl 1 thrallherd, lvl8 Dread Necro, 10 levels to play with.
2) Find a crypt, cave system, mausoleum, or abandoned castle/village/dungeon to use as a base of operations.
3) buy, or craft a Minion's Coffin -
http://www.wizards.com/dnd/article.asp?x=dnd/dx20021031x (if you can craft it, make multiple. Minion's Coffins are extra-dimensional spaces much like bags of holding, such spaces have limited oxygen supplies) and create a trap of automatically resetting desecration.
4) Wait 24 hours for thralls to arrive, order 18 at a time to enter minions coffin and close it behind them.
5) Wait 10 minutes for the thralls to suffocate and die inside, then open all the coffins and proceed to create all the undead you want through your own animation. (or place animating traps inside coffin, it has room for 18 corporeal undead, pretty sure a small trap will fit in there)
6) order the now 18 undead to come out and replace them with 18 fresh thralls.
8) repeat process till you run out of thralls, restart at step 4).
Or i guess you could create a magical trap of planar binding + dimensional Anchor and reverse gravity (which will last 1 round) (automatically resetting every other round within a temple with an evil altar. Thus the trap repeatedly summons outsiders, binds them to the plane, then forces them to fall upwards, then fall back down, then up, then down, repeatedly colliding with the ceiling and floor to take fall damage till it dies. Then reanimate it afterwards, voila, undead outsiders.
Edit: This would also require several autoresetting ghoul glyph traps as well.
Edit: Dont expect them to come out 'pretty' if your summoning demonesses ;p.
