It's so great that he's at least eating strawberries. They will be his lifesaver if you can supply him with enough. They have only a little nutrition, but have a lot of water, which he sorely needs right now. He may eat collards that are finely chopped and spread thin onto the cut/slightly mashed strawberries.
Iguanas can eat shredded raw hard squash. But cooking provides more nutrition and soft, cooked hard squash is sweet and more appealing to them. If the skin is tough, it has to be cut off before serving. Also mash the squash with a fork to make it softer.
Can you manage the UVB that Sue mentioned? It more than optomises his health. It makes it possible for him to live any length of time. Can you add the cost to the adoption fee? The new owner will need UVB anyway.
Give the adopter this, if he doesn't claim to be an expert:
I know shelter workers are always out of time, but it would help this guy a lot if you could tub him or sink him once or twice a day for ten minutes plus. It will help his skin, and it may stimulate him to drink again. Beware, igs always poop in their bath water. Also, they almost never have the highly virulent form of salmonella.