Happiness was, I believe, 15% or 20% with seven units there. The only thing I can think of would be to use the move cheat to move the big army I have into the city. Otherwise the most I can get there is two, maybe three units, depending on how many mercenary cavalry there are (even if infantry can make it, I'm not sure I can afford enough units to bring happiness that high. I'll try it though, and post the results).