MurrayPro Timecode Stamp is a fine little gadget for inserting VITC, BITC and genarating audio code from a video input. I had an application where I had to insert VITC into the black reference for an automation system to read. To disable the BITC I did this mod - see the video output stage schematic here.
First - lift pins 11 & 15 on IC1 (a DG611 video switch) so that the black 'hole' and white insert signals are stopped - short pins 6 & 7 of the same IC to ensure the black and burst goes straight through. The VITC is added later - see transistor Q1.