Well, the kindest thing would be for him to have at least 1 friend, a larger area to exercise, some sunshine (or in lieu of sun, full spectrum light bulbs during the day), variety in his diet to decrease boredom, etc. I didn;t have any luck with a mirror - years ago I tried that after my roo's much loved hen friend died (hoping that would help till I could find him a friend) and it succeeded only in stressing him out and he threw himself at the mirror to attack it and had I not been there, he would have really gotten hurt.
JJ
JJ