Oh Liz that sucks, I know from your posts that you would do anything for your birds which is why I suggested it in case you had never heard about it.
It is a bit bizzare about there being no new growth, they should start growing back but as you will already know they tend to get broken or not grow in properly because there are no other flight feathers to support the new growing one. I wonder if they have been pulled out somehow and it has damaged the actual follicules and that is why there is no regrowth but I wouldn't have thought they would have all got damaged if that were the case.
Obviously you know your bird best and I can't see exactly how the feathers are but it might be possible to attach the replacement feather to the shaft of the closest feathers rather than gluing feather to feather, starting with maybe one or two feathers at a time to see how Rambo reacts to it.
The only issue with that is if he takes well to it then he would need new replacement feathers each time they moulted out if there is no new growth

Like I say though, you know him best, it could be torture for him or it could cause him barely any stress if he is used to being handled but I think I would be tempted to start asking some vets some questions even if it does lead to nothing.