I was browsing through an old issue of Wireless World (really old - 1978), and saw this advert:
It's not very clear how it works, although if you look at the diagram at the very bottom of the photo, to me it appears like the elastomer is like a thin rod poked through the hole, and perhaps the contacts are pushed around it...or maybe it is a sheet of elastomer with small holes in it, and it is glued onto the PCB, because it says 4mm on the diagram, and a PCB would usually be much thinner.
Anyway, it looked interesting!
