Maybe freeze it on string so you can hang it up and it will take a bit longer to eat. I've frozen veggies in icecubes which they chase around as they melt so don't chow down on the ice itself much. Melon is super tasty though so I expect it would get a lot of interest. You could take it out a few minutes early so it's chilled rather than frozen if you're worried - it sounds like a good way to preserve it for spreading out over time.