"Reverse PRIME" support has just been added to xserver-xorg-video-nouveau 1:1.0.6-0ubuntu2 in Ubuntu 13.04 "Raring Ringtail", which should allow your NVIDIA GPU to scan-out to HDMI what's being rendered by the Intel graphics processor. Can you test with a daily build and report back?
"Reverse PRIME" support has just been added to xserver- xorg-video- nouveau 1:1.0.6-0ubuntu2 in Ubuntu 13.04 "Raring Ringtail", which should allow your NVIDIA GPU to scan-out to HDMI what's being rendered by the Intel graphics processor. Can you test with a daily build and report back?