We stay in Wincanton the night before, leave about 6am, backroads all the way and drive straight into blue/ purple carpark with no bother at all. Still stand in a queue for hours to get into the site proper though (last year particularly bad but I understand that was due to train strikes), but the car queues are a thing of the past.
Also ignore "road closed" for glastonbury signs if it gives you a shortcut, locals still use it and the stewards aren't checking your address when they let you out the other side.
Obviously that's cheating and it's on your conscience, but you can balance your Glasto-soul by chatting to a Greenpeace person and covering up any drunks you find sleeping in the sun.