I monitored SIX 3ds max 2011 installs with a bunch of various registry watchers, uninstall tools and other 'sniffers' with no luck. One thing is sure, the (real) 30 days trial process is well hidden. Before being bored, I decided to install Max on a 64-bit vmware machine. One click on a pre-install snapshot gives me the never-ending trial so I'm happy with that.
However, I'll be quite interested if someone got the solution which might be the same for Max2010 and 2012.