Franchises can contract their own soda supplier I believe.
crazylights, if you order a Julius, and they can't give you one, why would they ring it up so it shows on the receipt? Or did I not understand what you were trying to suggest? They're not going to let you pay for something they're not serving you.
The purpose of these shops is to determine if quality standards are met. If they can't serve up a Julius, just tell them they weren't available. Take a pic of the blizzard and call it good. You can't evaluate what they can't provide, so just do the evaluation on the part they could sell you.
They will accept handwritten receipts. Some really old DQ's don't use cash registers. The one I grew up with didn't have one. Just tell them you need it to turn in with your expense report.
Time to build a bigger bridge.