I'm sorry about the delay here, I had saw this thread, but actually forgot to answer, having another bigger problem with the game...
When I first launched the demo, I encountered the very same problem. The easy way to solve it is only to enable right click on the mouse preferences... (system preferences, mouse, and there activate the right click (couldn't be more precise, my mother language is french, and my mac is in french).
That just solved the problem. No remapping necessary.
It seems (and it's how Unity3D works, I myself toy with that engine for my own personal games I never publish :p) that Unity3D takes the keys, and reroute them through its own procedure, desactivating at the same time the mac os x property of simulating the right click with the command key (i hope this makes sense, that's not easy to explain such a thing in another language than your own :p apologies for that).
So the only way is to enable the right click on the magic mouse, and all problems are then solved, and the game runs smoothly.
If you are encountering the problem, don't remap, just be sure right click is activated ;-)