Does anyone here know of any good substances that might increase one's will to eat? I often wake up and don't even feel like eating despite being hungry.

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You have been preoccupied with what you eat and what to eat for a long time, What is going on?

Sun-dried mandarin / tangerine / clementine peels. If you have access to an Asian grocery store, you should be able to find them. Apparently, they could also be homemade, although I don't know if orange peels could be a substitute.

Yes, most people envy you.  But you really don't need anything more than willpower.  Open mouth, insert food, chew, swallow.  These are physical acts that you can perform by simply willing to do so.  Determine how many calories you should ingest every day and then set about making sure you ingest what you have planned.  If quantity is a problem, there are many calorie-dense foods you can take ... tablespoons of olive oil, spread a lot of butter on some bread, a protein shake, some tablespoons of peanut butter.  Since they're dense with calories, you don't have to eat a huge amount to get the calories you need.

Want to trade dietary weaknesses?  
This may sound strange, but Benadryl makes me hungry.  Of course, if the devil’s lettuce is legal in your state, you might try some to induce the munchies.

Unless you're malnourished increasing your appetite is not necessary and if it leads to gluttony should be avoided. 

I got the impression from other threads he's started that he's underweight.

I think there's more to the story because the gentleman has posted half a dozen times on this topic.  The advice never changes yet he keeps coming back asking the same question.  Perhaps it's a spiritual/mental/emotional situation that is unresolved.

Sometimes a good general confession can assist with persistent issues.  I'm not implying anything untoward in regards the OP.

So, for instance, if you simply took two tablespoons of olive oil (nearly 250 calories), three times per day, you'd instantly add 750 calories to your dietary intake.  Just think of it as medicine or a supplement.  Or you could also add some good cod liver oil (similar caloric content and extremely good for your health).

That much oil could make some people sick. Just a warning, though it might not cause any difficulties at all.

Fruit, veggie, nut smoothies might help. It's easier to drink fruity sweet calories than to prepare and chew a whole meal when you don't feel like eating.