Default [Q] Miracast to fullscreen in portrait

Hi,

I'm trying to screen cast from a Nexus 4 to a large screen TV (using a PTV3000). I want to put the TV in portrait mode and have the screen case occupy the entire screen, however I don't seem to find a way to accomplish this. When the phone's orientation is vertical (portrait) it assumes the TV is in landscape orientation and the phone screen is displayed small in the middle of the TV with black space on the sides.

After doing some searching it seems that this behavior can only be changed with a custom ROM, however I haven't been able to pinpoint where in the AOSP tree this behavior can be changed. Any suggestions are much appreciated.

Thanks!