how about a tennis scene? xd or maybe a shoe saloon...
How about showing the different colored shoes in a shoe store. Or just show some Inklings wearing the different shoes and just hanging about.
How about Crusty Sean advertising them at Shrimp Kicks?
An inkling getting ready to parkour
Try for a more action oriented pose, an Inkling jumping through the air while shooting (or flicking) with their weapon with their feet kicked out and closer to the camera. An angle like that seems like a good opportunity to show off the colorable underside of the Black Flip Flops.
Inkling doing jogging poster....