I'd be very curious as to what groups you think tend to show high fertility memes, and why you expect that behaviour to be stable in the very long run, and what evidence you have supporting that belief, if you do think it's stably memetically heritable.

Anabaptists, as I pointed out in my comment, show high-fertility memes. I suspect they have already selected for genetic high-fertility predispositions as well. (Peter J. Richerson and Robert Boyd wrote extensively about anabaptist genetic/cultural evolution in "Not by Genes Alone", which I highly recommend.) Anabaptist culture has thus far been highly resistant to the best modern superstimuli--in spite of the fact that their children are exposed to modern society through rumspringa and similar traditions. Therefore, it remains to be shown, by you, why future superstimuli will work (for every reproducing group) when all so far have failed. The vast majority of Amish children, for example, choose to remain with their communities instead of leaving.

The Amish population has been increasing exponentially for decades. They have shown an impressive ability to adapt to new economic models and yet maintain their unique identity, and resistance to modern culture.

Another group (which I suspect has gone even further than the Anabaptists in the strength of its memetic/genetic firewall) is the Mormon Fundamentalists. I've been intending to write a (short) post about them for a while, maybe I will get around to it soon.