You can try to press a small diameter stainless steel rod in the inside of the neck gooseneck tube.
1/8 or 3mm Dia. should do it.
did you get any pictures of how you did this with the rod for the neck, as I may want to do it as well, just not sure how to or what is the best way?
Did you get the m17 pivot post
No need to drill anything, just take the head and head bolt off and push a stainless rod into the gooseneck.