TerrainCollider.terrainData on custom mesh

Meshcolliders are slow, and updating them makes the game lag when an object has more than 1000 2000 vertices. So i would like to use TerrainCollider.terrainData on custom mesh, and i think only someone with amazing knowledge of colliders and terraindata would know, because unity hasn’t said if it’s possible.

How can i apply TerrainCollider to a custom terrain mesh?

I would probably convert the the mesh into a terrain (http://wiki.unity3d.com/index.php?title=Object2Terrain) and then use that.