I thought adding EDID - which is how monitors identify themselves to display sources - was going to be a difficult step.  (For VGA/DDC2, this is on pin 12 & 15 and uses I2C).  It wasn't...

Above, there's PaperBack letting a laptop (which conveniently has VGA built in) know its size, supported resolutions and timings.  (Yes, I crafted that serial number 'PNP4321'). 

I had SDA and SDL connected to the ATMega onboard the second board, and based my code on Rocky Hill's Arduino EDID emulator.  For the EDID itself, I used Deltacast's EDID editing application to craft a v1.3 EDID... but you could write a valid block yourself from the documentation out there.

Best Product Update

Unfortunately for PaperBack and me, we didn't make the Best Product finals.  Luckily, there are a few more rounds of the Hackaday Prize - wish me luck and perhaps I'll make it through to the finals in another round!