Of course, another good method is to find the heir, and, if he's unmarried and does not possess land of his own, to marry one of your female courtiers off to him, drawing him to your court, then give him an equivalent rank to what he'll inherit (Count if he's inheriting a county and you are a Duke, Duke if he's inheriting a duchy and you are a King, and if he's inheriting a Kingdom, don't bother). Sure, it won't pass directly into your dynasty's control, but he should remain a vassal to you upon inheriting the lands in question - I'm doing this to Hungary with the Duchy of Varna right now to slowly march up the Danube, since I don't want to do too much pagan bashing.