Well, now we know that we can put in techs for specific civs for advancement. So on Rhye's of Civ, as an example, Chirstianity/Islam/Buddahism/Jewish Monotheism can now be Required Techs, rather than Not-Required. (That would be a good way of testing this hypothesis).
Actually, do what people were suggesting in reverse. Have the People you want to hold back have the non-era tech and have that be the basis for a high-cost tech. You don't have the prereq, so you skip it, while they have to slog through...