Mark is actually a frequenter here at SM in the MEL forum. You can contact him through his book site:

Mel for Maya Animators

If he gives you an answer, please post it in this thread as it would be good to know. I was thinking there would be a simple way to do it through connections in the hypergraph but can only seem to make the typical parent multiple child relationships, not the other way around.

After a little more research, I believe you can do it through API/DAG (Directed Acrylic Graph). There's some documentation on it in the Developer's Toolkit section of Maya's manual but it's a bit too cryptic to me.