Without having play-tested it, I'd suggest:
1) More Orc slave units (4 max/1000) and/or
2) Goblin/Human slaves (6 or 8 max/1000) 2 attacks, 3 hits, 0 armour, 20 points
With a large number of slaves in the army perhaps, like Bretonnian peasants, they don't count towards the break point either, otherwise the break point would be huge! But they ALL have to die, like Dwarf Troll Slayers, otherwise the enemy gets the victory points?
Models for human slaves could be Bret peasants or Pendraken Peasants (code ELM14)?
Edit, maybe human slaves can be brigaded with Hobgoblins or Chaos Dwarves, with the humans always at the front of the formation. If they get driven back with Hobgoblins or Chaos Dwarves in formation behind them, they are destroyed (by the HGs/CDs!) instead of being driven back.