Well, in my case anyway, there was no "fascination with sneaking him in" anywhere. It just happened that I had to take him to the vet for a follow-up visit on the last day of a flooring sale. And I was buying flooring.
My choices were 1) Leave him in the car by himself -- which was not an option at all. or
2) Drive 15 miles home and drop him off and drive 15 miles back to go somewhere that is ACROSS THE STREET from the veterinary hospital.
I wasn't openly carrying him or walking him through the store. He was zipped up in his soft-sider. So the solution seemed pretty clear to me.