What life are you referring to? A standard fixture can grow algae, and any other life you will find on live rock.
No. Don't overfeed the fish. He's having a hard enough time as it is suffering through that ammonia that's in there currently.
It's really best to remove the little guy and use an ammonia source like a piece of raw shrimp from the supermarket.
If you want to keep him, then just wait it out. Eventually the ammonia will subside. If the ammonia kills him, leave him in there and let him rot away. the larger the initial ammonia, the better bacteria colony you will build.