No one has EVER offered or agreed to do anything like what you describe for DH. Not even once. They shrug their shoulders and move on. The characters care more about DH's shirt situation than the CMs at the stores that sell shirts. (seriously...he's gotten comments by WDW characters about his one or two Universal-themed shirts, and by Universal characters about his few WDW shirts, and they always think it's a serious bummer that the stores don't feel like selling much to a person who would LOVE to buy shirts) (he loves to wear shirts that are opposite from the park we're in...just like I love to wear my tinkerbell lanyard pouch on my Ravenclaw lanyard)
That said, DH has had GREAT luck at the offsite GiftLand! It's outside of downtown disney, sharing a parking lot with Waffle House. Looks SO cheesy from the outside, but they have real Disney shirts.
We have seen many shirts that we have just seen over at WDW, but for half price AND in extended sizes. It's where he has gotten most of his Disney shirts. Exact same shirts. So Disney is having them made...they just aren't selling them in their stores. It's mystifying.
The one place he found a zip-up sweatshirt was at OKW. He found another warm thing like that at OKW too, but wasn't in the market for it. At SSR he found a DVC fleece in his size and *maybe* one at the Grand Floridian.
Oh wait, DH says he found a couple at World of Disney, but he didn't like them.
But seriously, if you have any means of getting there, try GiftLand. They actually have a section for plus sizes, so you can go straight to the area.