Yes it is possible. Nothing is impossible. But the developers are not looking at it right now (as I told you in my last answer).
May be you should read the comments by Garth Wells at the bottom of this page.
https://fenicsproject.org/qa/1425/derivatives-at-the-quadrature-points?show=1425#q1425
However, you are free to develop your own independent model for plasticity using FEniCS and python as some people do. You are not necessarily dependent on FSM to create your model.
The documentation for FSM is in Ch. 26 of FEniCS book. If this clarifies your questions, please mark both the answers correct.
