Now this is a concern for Hemi.
Eating items like leaves can be a sign of nausea and if he is chewing on oak leaves these can actually induce nausea (and cause further harm if he eats enough of them). So, he is caught in a bit of a catch-22 here. Therefore, we need to keep him away from the saplings to start. Further to this, we'd want to try and address this nausea for him. To do so, you can try treating him with an antacid. There are a number of antacids that are available over the counter and pet friendly. Ones we can use here include Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid)or Zantac (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/ranitidine-hcl-zantac). Whichever you use, we'd give this 20 minutes before food to allow absorption and of course double check with your vet before use if he has any pre-existing health issues or is on any medications you haven't mentioned.
Once that is on board, you can try him again with the lighter diet options. Alternatively you could also offer rice with boiled chicken, boiled white fish, cottage cheese, or meat baby food (as long as its free from garlic or onion powder). Whichever you choose, offer small frequent meals to offset his stomach upset. And do avoid rich/fatty treats like bacon for the moment.
Overall, this is a concern for Hemi. His signs do support a possible infectious gastroenteritis, pancreatitis, or even dietary indiscretion (hopefully not a blockage since it has been 3 days since he ate the remote). So, we need to keep him from the oaks and start supportive care at this point. If you do so, but he isn't eating in the next 12-24 hours then we'd want to have him checked by his vet as he may need to be treated with injectable anti-vomiting medication +/- antibiotics to settle this for him.
All the best,