Go learn some code and do it for the rest of us for Christmas... because you know whats coming in January! SDK! I would think that you could probably work it in one of three ways:
1) The Caravan Food system I remember from one of the 'way back when' Civs. You could put a caravan in a city and have a feast, giving like 50 food or something.
2) Mess with the base trade system to allow you to choose one of the trade routes for each city (kinda like CTP used to let you do, except that was with all of them) so that you can send... well... anything, really. Hammers, food, whatever. Of course, there would have to be a negative.
Lower commerce output in that city would make sense, except that then you should really put that commerce into the other city. A cap on the number of routes wouldnt really be fair, because no rl cities have limits like that. Perhaps a geographical limit that expands with technology (for instance, no trades from cities that are further than... 5 tiles... until refrigeration).
3) Put a second automatic trade system in that deals with the food. Set a city to growth and other cities will send it one spare unit of food.
Or mix two and three together!
Back onto the topic: I am pretty sure you cannot settle on desert terrain or tundra terrain... but I could be very wrong...