I've extended the Away3D Mouse3DManager and MouseEvent3D classes to accept the right click and middle click events recently added to Flash Player (Novemeber 2011, I think)
Remember to update your compiler and target Flash Player 11.2 or later. I had to do a bit of mucking about in FlashDevelop to get it working myself, which may well explain why it's not yet in the official Away3d library. Here's a really crazy, wild demo to show it works...
(Click image to open demo. Click/Scroll on ball to see events triggered)
And here are the files...