hhhmmmm I think modding the game is about the only way you can do it, unless your a faction right next to them. Like once I played as the elmoheads, I unified Spain, and then I took Egypt and palestine. The Egyptians fell into rebellion and were left with only Arabia. I withdrew to Cyrencia, but built a citadel with a few hundred order foot soldiers(massive bribe) in Palestine. The turks were quick to jump on the rebels and they're armies became impressive quite quickly. Soon they were all the way into Egypt, but they didn't attack me in Palestine, as we were allies. But as soon as they were in Byzantium, that changed. They soon became a superpower and I was hard pressed to hold them off. However they pushed all they way into hungary in the meantime. Usually the turks get killed off within the first 50 years. But since I was there to weaken thier neighbors they were able to grow a bit and posed a much more intersting challenge.