Things are progressing now with Roger, which has brought to a point where I have to confess a secret I've been keeping,not because I'm ashamed just that I don't know how peeps will react, so here goes:
When the vet offered the T4 therapy to induce a moult he also offered another option. He offered to remove the clipped feathers under sedation, and I went for it after
@fashionfobie suggested the implants. I've heard about this before and I know sometimes a bird will pluck a damaged feather to replace it. It's more natural than a chemical therapy, quicker than waiting for a moult, relatively painless, and considering he's not a companion bird and needs to fly I think the right thing to do.
It's paying off. Today he came out of the cage for the second time ever, and he took his first ever flight. I knew he was going to, he was pacing to and fro by the door twitching his wings. His flight was level for 6 feet and finished with a skid.
I'm happy with that decision now.
I don't care if he never sits on my hand, or never steps up. So long as he feels safe enough with me to come out of the cage and enjoy some wing time I'll be happy. If at any time in the future I get concerned about his wellbeing I will consider other options.