I don't think it's possible to win two more units without taking unnecessary risks.
By the way, in online play, I don't think it's worth taking this starting position on the first map. The morale of the angels is only scary in the first round, and in two dozen battles, it hasn't happened even once. But the horned demons almost always used their morale ability creatively and effectively, making it difficult to avoid critical losses.
I managed to complete the demon map, losing 3 air units and a few pikemen, but when I tried to take the starting position on the angel map, I lost both cavalry units. :(