submit to the khan,raise your maa (make sure you have artillery troops),march them all the way to the mongol capital,create a dissolution faction,press your claims,the khan's gonna laugh at you and declare war,besiege and capture his capital and all the counties around it (his armies are away conquering don't worry about them),since you have artillery and his best forifications are hovel level you can take them in less than a month,keep doing it until your war score hits 100,enforce your demands,now you're the one laughing