But I really wouldn't advise using a Hol-ee Roller ball for a BP, because where their head goes, their wider body can get very stuck & you'll have to cut them loose, which could be quite dangerous for your snake. Better to shop for those in person too- to make sure the holes are much bigger than your snake.
BPs are a little harder to entertain, because they don't explore so much- they're not active hunters & wait for darkness to ambush their prey. They're actually quite vulnerable to predation themselves when out in the open, so I wouldn't over-do it- you can stress them out without meaning to.
Corn (& other rat snakes) like to climb, so fake trees or anything with similar arrangements (like some types of coat racks, for example) can be good for them. Some people build a "jungle gym" out of bamboo poles tied together with ropes, or out of PVC pipes joined with the "elbows" sold to join them. Ladders can also work pretty well.