Yeah, the moss would be a pretty good idea! Maybe a layer of sand to get it to grab on.You could also cheat and just coat the hose / pipe in aquarium safe silicone followed by a layer of sand, stones, rock, driftwood pieces or basically anything you like, that suits your tanks scape...
The other option would be to try and get some moss attached and growing across the pipe for a more natural look...
Both methods should save you some substrte lol...