As someone who trained my dog to sit and wait for me outside a shop while I got coffee, which was a similar delayed gratification and I didn't even use treats, I think science might be underestimating just how stupid human children are.
1. Draw a triangle on your forehead
2. Make a shitty clone of yourself with a circle drawn on the clone's forehead, who comes out of the shop immediately after you walk in
Then see if your dog decides to follow the shitty clone, or whether it waits a couple minutes for the regular version of you.
Edit: also, repeat with many more dogs, many more dog owners, and many more shitty clones.