Workaround for Non-convex MeshCollider cannot be used as a trigger in Unity 5

What is the best practice do deal with the issue trigger being non-convex mesh in Unity5? There is a project previously made in Unity4 and we want to get it working.

To be more specific we have several mesh colliders in a shape similar to donut and used them as triggers. But in Unity 5 we get

Non-convex MeshCollider cannot be used as a trigger in Unity 5. If you want to use this mesh as a trigger you have to make the MeshCollider convex.

One obvious method is to change meshes to be non-convex.

Thank you for your suggestions