You might find more help on a forum dedicated to dog training/behaviour a good one is
http://ttlntl.co.uk/forum
they have lots of helpful people who are trainers/behaviourists (many have helped retrain/rehabilitate rescue dogs).
As he will only accept food off you I would say you have more of a deep rooted problem than one of a greedy dog who bolts his food.
You could have problems if for some reason you cannot be there to feed him, what if you have to put him in kennels for some reason? Or he has to have a prolonged stay at the vets?
The above site is very friendly and you will find caring help and advice with any problems you have.