Really? You're not creative (or mean) enough. Two options off the top of my head, I think they may have been mentioned earlier in the thread.
1. Have the lord of his region switch realms. This works best if you can pay them off with a better region on their return.
2. Give away their region. They'll still be in the realm, but they won't have any income. If he's a duke, have his lords switch lieges and then disband his duchy.
3. Put a 1000 gold bounty on his head, and then announce to all infiltrators that any infiltrator caught assassinating him will be released immediately with no repercussions. Notify him that you have done this. Repeat until he leaves the continent.
4. Get together with your ally (or possibly, enemy), and have them declare war on your realm (or you on them, whatever). Continually provide that realm with the location of the royal, so their army can harass him. If he has a region, have them loot it until it rebels. Use your own priests and diplomats to help the region revolt, and have surrounding lords drop their tax rates in order to make his peasants even more unhappy. Refuse to sell him food (or buy his food, depending).
1. This is abuse of game mechanics. Anyone I saw doing this I'd immediately report to the Titans.
2. They are still in the realm.
3. This still requires the noble to leave on their own. You aren't forcing him out. Instead you're dumping tons of gold into endless infiltrator hits which don't actually do anything, since infiltrator assassinations can't even remove people from positions. (I've already asked and no one can remember the last time an infiltrator has done this)
4. I consider this either abuse or against the social contract as you've pointed out. The food part is reasonable but still doesn't remove them from the realm.
