I think you could epoxy/bond the anchors to the existing glass and if you turned them carefully it would probably hold them long enough for the anchor to expand. There are also many different styles of those, one being a toggle bolt that may work. You might have to go up in size if the hole is wallowed out. Just a few thoughts having had old boats most of my boat owning time and having to keep them cobbled together. Good luck!!
See you on the lake and have a great day!