inner trunk drop off drain plugs

Sorry for no pics, but just wanted to ask any of you who know how to put those pesky metal drain plugs back into the inner quarter panel drop-off area?? I cannot get them back in, and I already poked a hole in one of them while trying to hammer it back into the hole. Can I use rubber plugs instead? I am looking at every hardware store in my area and they don't have anything that may work for this application. BTW, my Nova is a 1970. Any suggestions appreciated.