Raid,
What I have done in patching curtains is to glue the smallest thinnest possible piece of new shutter curtain material to the curtain over the pinhole. I've glued the patch cloth side down, rubber side out.
I use the thinnest curtain material from micro-tools.com, which is thinner than the original curtain material from my Canon IV. I glue it with pliobond also from micro-tools.com.
I use a hollow punch 1/16 - 3/32 in diameter to cut the patch. With two holes next to each other, I cut the smallest rectangle I could.
In my long illustrious career of patching curtains (5 total), all have held. 😉