I just run offline. My gaming machine isn't internet-capable by design. Most properly-written apps, once they detect that there's no network available, will simply move along. You can accomplish the same thing by unplugging your network cable, turning off your switch/modem/router, running IPCONFIG /RELEASE from Window's Start->Run menu (the preferred method), or a number of other ways...
On my previous system, I simply told the firewall not to let Trainz or any of its application pass through and what i got was CM with a permanent red bar across the bottom edge and relative stability.
As has been mentioned before, the whole validation mechanism needs a rethink. Don't want to reopen the other question of whether it needs to be there at all but just how it is implemented. This total reliance on being able to reach a server somewhere that could be offline for any number of reasons should not cause the local game to malfunction if it can't be reached.
Me I generally sidestep this issue by having next to no DLC, mainly my own objects and some from the DLS and third party sites. I noticed a few validations, about 90, today in CM3.7 but it never interfered with launching Trainz itself.
