Question and Possible challenge for a dev if poss! :) topic

Okay, so heres the deal, i own a shield portable, and a shield tablet, but heres the thing, i dont have a wireless controller for the shield, i do want one, but i have a xbox one controller ps3 controller and i can get both working on the tab, however, i want to use the nvidia gamepad mapper for a non nvidia controller, but you need to hold the start button to bring up the mapper....

Anyone have any ideas on how to do this and access the native nvidia game mapper without an actual nvidia controller connected?