[ODE] Recommended methods for simulating a circular platform?

[Riley Lark]

I hope to have a circular platform in my simulation, but the only
cylinders included with ODE by default are capped.  What have others
done when they actually needed a flat, circular surface?

If it comes to it, I may be able to write my own implementation... I
only need to collide spheres against the cylinder, and the cylinder
can always be aligned with an axis, but I was hoping for a better
solution.

Thanks for any advice!