Man that looks like a tough fix. All the alternatives you have mentioned will build up too much thickness. You will still have to take it apart and sand it down really flat to not have friction on other blades or you might risk binding or even creating another pinhole. Friction would also affect speeds.

I you get it apart, maybe a coat of paint across the entire surface of that blade, can patch it on both sides. The paint would be drawn into the hole. Durability would depend on paint type and thickness.

Try finding another shutter or parts body to do a swap. Thats the sure way. Patches even if they do work, may fall apart and end up binding the shutter anyway.