title: Python & scikit Learn: replace matrix vector product during training with custom call
body: <p>I've looked through the documentation over at scikit learn and I haven't seen a straightforward way to replace the matrix-vector product evaluations during propagation with a custom evaluation call.</p>
  
  <p>Is there a way to do this that's already part of the API...or are there any tricks that would allow me to inject a custom matrix vector product evaluator?</p>