I feel exactly the same way.
This may sound a bit square, but I was reading an excellent solution to this problem in a design journal the other week. The author proposed inclining the area immediately next to the conveyer belt, to make it awkward to stand or keep a trolley on. There were a few others also, but this was the main one.
I see the same thing at the 'take a number and wait your turn' gig at Coles/Woolies.