Believe it or not, these exist. However, they all have something in common: They were not constructed as Casey’s gas stations.
I have now run across two of them. One is a former HandiMart at the I-80 US 151 exit. It’s a small building built in the Amana German style. The other is a former Holiday station in Spencer that is across the street from another Casey’s.
The Holiday gas chain exited the Iowa and Nebraska markets with the sale of 10 stores to Casey’s in 2010. If you go to the Holiday website state-by-state list now, there is still an option to select Iowa and Nebraska, but the store list is blank. Every state except those two has a map image without them (e.g. here).
One of the other Holiday stations is at the end of I-380 at Mitchell Avenue in Waterloo.