If you don't need this to be interactive then it's very easy to set up an animation of the balls sticking to a magnetic cylinder. You can even use hook's law so the balls can build a chain that is effected by inertia and other forces you may want to introduce. Also the balls would be able to detect self collisions so they won't go through each other.

If this needs to be interactive then I don't know how to solve it. The latest beta messes up physics on my computer. But it's got some important physics functions like the iteration control and the physics auto off feature. I know I messed up the names but I'm hoping you know what I'm talking about.

Anywho, it's probably worth while to wait for these functions to work in the physics system.