how to extract FEM matrices from structuralModel

I created a structuralModel using

createpde('structural', 'planestress')

I then assign a geometry, specify coefficents, etc, and solve the problem. I would like to have access to the stiffness matrix of the Finite Element model. With PDEmodels that are not structural, i.e. were created with createpde(), I can acheive with

assembleFEMmatrices

However, this does not work for structuralModels.

Is there a way to get the FEM matrices?