Here's an idea I had. It's not really feasible since the heat sinks aren't readily available and would be crazy stupid to custom make. It was fun to put it together in Sketchup though.
When you put four together, they create a tunnel:
I got over my Apple obsession years ago, but I still like to keep up on their new stuff. You seen the new MacPro? The round one? It's new "Unified Thermal Core" uses a triangular heatsink that splits the heat between the CPUs and GPUs, and blows air up thru the center. Very similar to the idea you have here. When you put four together, they create a tunnel:
I would consider this worth looking into more.