If he is getting a decent BARF diet, he should be getting all he needs anyway ( there is BARF section on here, with loads of more advice ) - if he isn't keen on dry, it can be a struggle to get them to take it regularly. If I take my lot away for a couple of weeks, and there is no facility to store BARF, then they have dry, but I usually end up having to add gravy/chappie/cod liver oil etc to get them to eat it - and even then they are not impressed.
One thing that helps, is not making a fuss over it for the dog - put the food down, and if it isn't eaten in 15-20 mins, take it away again