I enclose a photo of a typical board, I don't have G-Code for this so if I wanted to drill I would mount on base, program some fixing points and then follow a line which I would draw on photo and mark each hole in the program also use different colour pen for different drill sizes on the photo, and then generate G-Code from this to drill.
I suppose you could do manually but would take forever on a board with say 1000 holes or more.
Regards john