LOD group questions

Is there a way to make a LOD Group http://docs.unity3d.com/Manual/class-LODGroup.html work on distance from the camera rather than percent of view frustum? The documentations says "The percentages in the LOD bars represent the fraction of the view frustum depth where that LOD level becomes active" but i found out the percent is relative to object size and it has become a nightmare to make all the objects in scene appearing and disappearing at the same distance from camera.
Second question, is there a way to use something (a script or a shader) to make the appear/disappear event more less obvious to the eye? A transition between LOD levels will also be nice if it is possible.