I assume at this point you have more or less unlimited money, so begin the strategic bombing:

1. Blockade all ports.
2. Invade with spies/assassins and sabotage the troop and economic infrastructure. Pretty much every city you have that is not making troops should be making assassins and spies (and the boats to transport them) and pumping them towards the Nile.
3. If you don't think you can hold a city, take it, exterminate it, retrain (if you have time), loot it, and leave it. Repeat on another front. Gift cities back to them to prevent rebel uber-peasants, and they will have to spend money to rebuild.
4. Find less defended cities in the backfield to attack or bribe. Burn these as stated in #3.
5. Bribe their generals and use them to create merc armies behind the lines. Definitely buy all mercs to keep the Egyptians from getting them, even if they are just cannon(chariot) fodder.
6. Siege cities whenever possible, even if you can't take them over. Disrupts build queues and econ.

Against Egypt, no tactic is too cheesy or underhanded. Use wardogs, elephants, onagers, whatever you have to do. They deserve it!