Hey!
Since the latest update your imported model can be completely excluded from picking by setting the property "Pickable" to false;
But you're right to assume that an imported model with different meshes can currently not be altered separately.
I just noticed a related issue with picking against imported models. For submeshes it will actually return NaN and therefore won't be really useable. It's clearly something to think about for the next little maintenance update.
With the addition of a general mesh visibility action your suggestion would become fully feasible.