Sorry but thats not neglectful, that is abuse.

From the little I know Harlie came from a home like that, possibly much worse. They would bang on the cage, shake it, poke stuff in through the bars at her and she hadn't been let out of her cage ever and couldn't fly because she had no muscle. For the first couple of months she would flap round her cage screaming if I even entered the room never mind went up to her.
Anyhow you do right, sit outside talking to him. Millet is good but too much of anything is bad so try to offer other stuff he likes too if you can. Don't push him too hard as it will be easy to destroy any small amount of trust built up but don't be too scared to push him a little either (just go straight back a stage or 2 if he reacts badly).
Sorry but no not really, there isn't any other way to earn trust. Some people use flooding methods but I cannot agree that is an ethical/moral way to go about it when there are much kinder methods.
I have worked with birds as terrified as Harlie before and they all tamed down much faster (within a few weeks to a year). I'm on my 5th year with Harlie now, she has come such a long way but there is still a long way to go. She will do certain things but I still cannot push her much or we are right back to square one (almost).