All right, all right.
Well, the first thing I do is add a new difficulty to the list. I just copy and paste any difficulty ("Noble", preferably) in the Handicaps XML and rename it to something else, like "Custom". Then what I do is adjust the barbarian spawn values in this new difficulty (although I could be wrong). Now I think Raging Barbarians merely doubles the number of barbarians on the map as well as turning off the culture barrier. So I double the unowned tile:barbarian ratio to halve the number of barbarians that normally appear, and then switch Raging Barbs on. This doubles (again, correct me if I'm wrong) the halved amount, resulting in the normal amount of barbarians, but they can now enter your territory as soon as they spawn.
I'm still tweaking it, though.