Combine common surfaces

I have a problem with throwing ball across few game objects (platforms) that are connected. Platforms have flat parallel surfaces connected by "V" shortcut, so there isn't any step. From time to time ball is jumping on platforms connection like on small step. Adding rigidbody, changing mesh collider to box colliders, setting convex and using CombineChildren script doesn't work :( Propably making something like this will help:

But how to do this in editor or with script in runtime?