The problem is getting to the backside. And more importantly, getting all the crud out thst caused it to rust from the inside out. I'd suggest cutting out a square to get to the inside, try to vacuum out all the crap, then patch the hole with good metal.

My quarters had a good 4-5" deep pile of dirt, rust flakes, etc between the outer skin and the inner panel. I couldn't access it till I cut the quarter off.

Plus, the inner panel will be just as soft and rusty and needs fixed too. It's easiest to remove the whole quarter to find all the hidden rust, fix it, and patch the quarter and re-use, or get a new quarter.