A good rule of thumb, if there is a TS location, they won't offer any discounts at the CS locations. The Values, POFQ, Artists Palette (the odd man out here) and the AK locations.
The card holder doesn't need to pay, they just need to be at the meal. So you could possibly trade off meals? You pay for one, they pay for the second. Or they just toss some cash on the table to cover their portion. That works as well.
Edit: The official rules do say that the card holder needs to pay. However, I haven't had that problem personally.