Full disclosure: The Romney campaign (which I support) is doing much the same thing. If you give $5 you are in a drawing to have simple (probably brief) lunch with Gov. and Mrs. Romney. It is a way of having a few “winners” act as representatives of everyone who gave. Could this also run afoul of gambling laws?
If I were in such a pool of donors and won (thereby becoming a donor-diner), I would be glad to pay for my own hamburger, if that would satisfy the legal requirements.
I think you need to read the fine print. Where Obama stepped over the line was not allowing any way to enter without sending a donation.