Workaround to Non-Convex mesh colliders with non-Kinematic RigidBodies?

Hi!I am reatively new to unity, and have just begun experimenting with importing 3d models. I have created a very simple model in sketchup, of a 3/4 circle, the other 1/4 is simply removed. On importing the model, i found that in order to use physics, as a non-kinematic rigidbody...my mesh collider must be convex. However i can't do this, as the collider will not account for the removed 1/4 of the circle. Making it kinematic is not an option, as it needs to move around with added forces and such.

Has anybody found a workaround to this, and does anyone know why this restriction is in place? I'd love to know.

Any help would be appreciated, Thanks!