Autoreject calls via predefined SMS message while away from phone
With SL4A or Qpython (Python Script Engine) you can use android apps permission .(E.g With it you can send mesaages, take picture etc.)

If you have basic knowlege of python you can make a script that will help you to do that.

You will also need tasker etc. To launch script

[I think it will be hard task to do it.I just gave you the Base Idea.Hope you will make it]