After a fair bit of practise, I managed to get over the invisible walls into the area you overlook at the start of the game. Used a Monarch with maxed boost but might not need this. I think clipping the wall on the left gave me an extra boost to get over

http://www.youtube.com/watch?v=qIgeVOeqaKI

Awesome! So those invisible walls are actually real walls that you can get over!