If you are concerned with cleaning being difficult, I would stay away from substrate. It will tend to be more difficult to clean than just a bare bottom of the enclosure. I would use paper towels if you are looking for quick clean ups. This will also stop the water from pooling and still help maintain the humidity levels you want. There is the possibility that your chameleon could eat the substrate as well. I know my little veiled started eating the moss from his first enclosure and had quite a difficult time passing it. I was lucky he was able to. I would just get a routine of cleaning a couple times a day if needed.
If you still want something on the bottom, they have that green reptile carpet that you can place there, and just switch out with a new piece every few days. They can be washed and reused.
If you are talking about a 2 year old male, how much are you feeding him? He probably wouldn't be pooping that often, so I wouldn't think this should be too much of an issue.