I typically come into the store around 9:30pm every 3-4 nights and this is what I see in the hot food section.
There's an awful lot of delicious looking food sitting in those warming trays, and very few customers buying it. Your employees have indicated that it all gets thrown into the compost pile at the end of the night because donating hot food comes with a lot of legal risk, which I understand. But I believe there is way more value in that food...
What if every night after 8pm, you charged a flat rate of $10 per plate with all proceeds benefiting the Whole Planet Foundation? The majority of that food was going to get tossed into the compost pile anyway, so why not put it to good use and turn it into a positive thing for your organization?
At stores that serve alcohol, like the Plymouth Meeting location, you could even host happy hours around it - you'd get alcohol sales, the organization gets the food plate money and awareness. It's a win-win!
At the very least, it might be worth experimenting with this concept to see how it impacts food sales and traffic numbers.