You can do this in the following way, however be warned that it's a bit fragile. You can't edit the geometry after this, or delete the history.

Once you have all of your blend shapes connected, simply combine the target head and the body into a single object and smooth the normals. The history dependency will keep the blendshape intact.

A better way would be to write a script that would take the vertex normals from overlapping vertices and average them.