I sat S2 last week.
They are right, there is nothing you can do to prepare, IMO.
Use the time they give you to practice the tests as much as possible. Even if your fellow test mates are whizzing through doing the actual test, don't feel embarrassed to be sitting there practising, they're not gonna pass the test for you, you are.
Just get a really good nights sleep the night before, a big breakfast and make use of the free coffee and lunch they give you. On your lunch break they usually arrange for a controller to come up from Swanwick to sit with you and answer your questions.
To be honest, you could have found this info in the Nats Interview sticky at the top of the page..
Good luck, S88