I've recently gone through the day of computer tests, which included the FEAST tests, it was a far from pleasant day and I'm confident that I failed to get through. There's nothing you can really do to prepare for the tests apart from practice your cubes a bit more because they make an appearance. My only advice is to read the instructions for each test very carefully and do the practice questions as many times as you feel you need to. When I turned up for stage 2 none of us had been informed that the system had changed to a day of computer tests, we were all prepared for the motivation paper and HR interview so you're lucky that you at least know what to expect on the day. You still do the old format computer tests aswell which throws you a bit because you go from using the mouse on the new tests to using a specialised keyboard for the old tests, it's much easier using the mouse.
Best of luck to you.