My Border Collie was the same. I tried removing the food after 15 minutes and tried encouragement etc and she went almost a week with very little food. After a trip to the vet we found that she has Inflamatory Bowel Disorder and at certain times she will just go off her food altogether. The vet then got us to start feeding her some yoghurt (along with her medication) and now she has a tablespoon of yoghurt with her dry food every morning and can only eat lean human quality meat (steam chicken etc) and nothing raw.
We have recently switched to Science Diet Sensitive Stomach dry food and she seems to eat that with no problem at all.
My suggestion, add a bit of yoghurt to the dry food and see if this helps to add a bit of interest to the food whilst also being a good for the pup.