Hello!~Sorry for the delayed response.

There are ways to work through this, but I would highly suggest nipping this as soon as possible. As you do not want it to become a habit for the dog.

First and foremost you need to be working with a tired, hungry dog. Lots of exercise prior to ANY food behavior modification training. Reason being is the dog will be more clear headed and inturn easier to work with. 

First off, do you ever fast your dog? Also do you have any other dogs in house? Please explain to me your set up, as well as feeding rituals.