Out of curiosity, do you use dynamic index buffers to accomplish the geomipmapping, or do you just trample the vertex buffers every frame?
There is only one vertex buffer per patch that contains all of the vertices. Index buffers are being used, all of them pre-generated of course and uploaded to the graphics card. Rendering a patch then becomes a simple matter of selecting the right index buffer (or index buffers, since stitching requires more than one drawing call).
Ah, nice!