Dave, I will take a stab at this. Haveing not had the opertunity to be stuck in such a jam. I would take a piece a aluminum and cut out a whole the size of the shield.The aluminum plate should be the size of the board or larger. Use stand offs to raise it above the board. This should protect the rest of the board from reflow temps. I would place the board on a pre heat table then to remove the shield use a standard heat gun? Ok, the heat gun part sounds a little scary but that's why we just had the metal shop make us that wonderful aluminum plate to protect all the other parts. I would then try a vacuum pick up to get the shield off the board. I'm sure there will be a lot of laughing at this aprouch but I think it would work just fine. I know for a fact the price is right! I was under the impression that the shied was solid? You didn't say. If it wasn't solid and the screen kind, I would just hack it up with my moto tool or some nippers and desolder with my iron. Then rewash to get the dust out.
Hmmmmmm? Just had a thought....lol. It's late I can do that? Did you consider resistive soldering. Turning the whole shield into one large heating element till it kicks free? I would try it on a pre heat table as well. I think that's the ticket Dave. The whole thing needs to heat evenly or you will have a hard time protecting the parts under the shield. I know the heat gun thing would work but there's no telling what the shape of the parts would be after you lift the shield. I think you could control the resistive unit better. I would pull the tweezers out and run some wires with aligater clips or what ever would work. For never haveing done it, that's my best........Jeff