Ummm he already made it have gamepad support.
Just download the latest version and load it.
https://bitbucket.org/eke/genesis-plus-gx/src/master/builds/
I downloaded this "dol" file and replace the original from the genplus-gx-1.7.5-RC1.7z file.
I started the emu but I got no WiiU Gamepad support (WiiU -> Wii -> HBL -> genesis-plus-gx)
I can only select the wiimote in the controls screen
Any help, please?