Could we use the ATmega8u2 isp port for this function (as programmer master)?
Well the 8u2 certainly has enough I/O pins available and already has a usb connection to the PC, so it would just be a matter of a few wires and of course the real challenge would be the software changes/additions to the 8u2 firmware and the Arduino IDE. Not sure it would be something the Arduino team would be interested in taking on but some user contributor might get inspired to take on such a challenge.
Lefty