This does not exist: "how to treat the markup portion the meals would have cost if sold to customers."

You don't get to write off the potential profit. There would be nothing to stop me from stating, "That would have been a $1,000 steak!"

"According to the article"

Which doesn't seem to apply to your facts and circumstances so far. It describes my example: giving to a Charity and the Charity then uses it for Charitable purposes. Not your client as a restaurant "giving it For Charitable purposes" by handing out free meals.

"the charitable deduction under this provision is 50% of FMV but it gave no guidance as to how to do so."

Example: a farmer provides foodstuffs to that same Food Bank, which is a qualified Charity. The Food Bank uses it for charitable purposes.

Can you find your restaurant in any of this?