If you have weekends off could you go up there a couple of times? Go on up and shop up there and leave him with healthy choices that he likes that are easy to prepare?
When I was here alone I basically lived at work with side trips to the barn and there were times I was horribly lonely. Going "home" just made it worse so one year DH and DD came out from Thanksgiving to New Year's and it made me feel so much better. And yes, I wound up with cheerios and oatmeal in my cupboards!
What about getting him to read just one book about eating/health? Personally I like "Why We Get Fat" by Gary Taubes, or Wheatbelly by Dr. W. Davis. I'd say, "look, you don't have to listen to me, but would you please just read one thing for me, that's all I ask". And give him the book.