SimonTheBeetle: If you're REALLY in the "play flash or die" mode, the easiest way of doing it would be to get yourself a VM, install an old OS (even XP if you have to) in it, block all updates, install any old browser of your preference plus a decent anti-virus program as a minimal protection measure, and do nothing but play the game in there.
Good point. I actually thought about that this morning. Oracle VM VirtualBox is a good free one.
Only thing is, you'd have to have a licensed copy of your OS to install in the VM. Last I looked, a lot of current browsers don't support Windows XP, so if you went the Windows route, you'd probably need to install a more current OS than that.
You could always run some flavor of Linux in the VM as your OS (since Linux is free, unlike Windows), but that's way beyond the capability of most WGT users, I think.