Spherical World Physics

I am creating a game that will use a spherical planet which the player can traverse around. It will be divided up into cells. This could be acheived with flat terrain however there are a few reasons for which I would rather use a sphere.

I am planning to use ODE for physics and collision detection and the example by ynjh_jo was extremely helpful as were many other examples in that thread. The problem is that the rigid body physics are all designed to work with gravity remaining in a constant direction (Or so I understand). My question is could anyone recommend a way to acheive rigid body physics in a spherical world?

just apply your own gravity that is aimed at the center of the sphere all the time. I think there was an ODE magnet thing you could stick too but i just be confusing it with my own contraption.

Aaahhhhaaa thanks to your words of wisdom I have a semi smart idea! Hopefully I can get it working within the next few days coughMonthscough.