You might be able to use an ActivityStarter to command a handwriting app . Google Handwriting Input is a stand-alone keyboard which allows you to handwrite text on your phone or tablet. This thready discusses how to launch the handwriting app that you install on your Android using ActivityStarter. Activity starter to launch google handwriting input
Yes, it might be used to interpret a handwritten A to a but you will have to figure out how to interface the google tool to your App Inventor 2 app.