I have been able to achieve it with very little changes:
background water sphere uses material with standard shader and Transparent rendering mode
continents-only sphere material render queue is set to Overlay
I just phong tessellated the whole thing and added this to fix the normals:
#pragma vertex:vert ...
#pragma target 4.6
void vert(inout ...
You can upscale the earth model, subdivide the larger triangles that end up underwater and make sure the new vertices are all the same distance from the center as the existing vertices.
There are 2 ways to add a vertex, in the middle of a triangle where you replace that triangle with 3 new triangles each bordering one of the edges of the old triangle and ...