I've been pondering this for a while. It's an interesting one - most of the support heros feel less useful with Nagash present, and the units are very expensive so you don't get much else with the big bone boy.
Here's where I've got to so far..
Petrifex Elite
Nagash - 880
Liege Kavalos - 200
General, +2 wounds, Ignore 1st wound per phase
20 Mortek guard - 260
10 Mortek guard - 130
10 Mortek guard - 130
6x Necropolis Stalkers - 400
Liege Kavalos gives you a quick unit that's pretty damn durable (2+ RR 1s, 6++ & ignore first wound) which I think the list is otherwise lacking. Nagash does his thing & casts lots of spells. Mortek guard take objectives and are tough to shift, while the bigger unit is a decent threat, especially with buffs. The necropolis stalkers are a fairly quick and hard hitting threat to use as a counter attack unit, but could also be replaced with the Immortis Guard if you fancy instead.
until