“or somehow defining this situation as the Mechaber’s “??? ?? ???” case and eating before davening based on that…”
I would go with that. Personally, I usually have stomach pains if I don’t eat something right away in the morning, so since I wouldn’t have Kavana, I rely on the S”A. It’s hard to believe that after 14 hours hours of fasting and being wiped out from a hard trip like that, that you wouldn’t fall into the categories of Ra’ev and Tzame. S”A is mattir lekatchila as long as you don’t have kavana, although you still have the choice to not eat and pray if you would like to (even without as much kavana).
About davening before netz be’yochid: I would think that this is not a real Sha’as Ha’dchak. In 89:8 the M”B mentions sha’as ha’dchak such as going on the road in a scenario where you won’t be able to have kavana. Based on what I mentioned before that you are allowed to eat if you won’t have kavana, there is no heter to daven early.