Maybe some games (not wildly energetic) will tire him out so he will sleep more. Training tricks will cause mental tiredness as well as physical tiredness. Look at
www.kikopup.com for ideas for clicker training. Use chew toys like a kong filled with his meals and sealed with peanut butter so he has to work for his food -- this will be more tiring than just eating out of a food bowl -- and if you scatter small pieces of dog kibble for him to search for, this is also more interesting than just using a food bowl and while he is hunting food he won't need the cone on as he will be concentrating on something else. Lie him on your lap and do some gentle massage while he has the cone on so it is associated with a pleasant experience. Good luck!