In a mixing bowl fitted with the paddle attachment, or by hand, mix together the cake crumbs, cocoa powder, powdered sugar, and nuts. Stir in the 2 tablespoons of honey and the rum. Using your hands, try to form the mixture into a ball. If the mixture won't hold together add a little more honey. Roll the mixture into 1-inch balls, then roll them in powdered sugar or melted chocolate, and let them set up. Then, let them age or ripen 24 hours.
I toured Sara Lee Bakeries when I was a kid and they had scrap bins in laundry carts but it went to a local pig farmer. I used to make these in my bakery to use up all the trim from my cake layers. We kept a 5-gallon bucket, as most bakeries do, where we throw all the trims and once a week make rum balls. So each time, they were a little different depending on the content of the scraps.