Ok thanks.As far as I'm aware, there is no tool that creates virtual buttons on the touch screen. But going by the assumption that your friend has a 3DS with custom firmware, he can use the tool NTR Redirector to control the buttons of his 3DS using a PC (which you can in turn connect an external controller to). He could either use the original version of NTR Redirector or the one built into the multipurpose tool 'KitKat'.