i think he's saying use the trade offer screen to put a bundle of food up for sale at certain price. (and get the other lot to send caravan)
never tried it, no idea if it works. i do know if you do a autosell at X gold for all bushels above Y food, then it gets put into trade balance, so it's obviously not that.
but if it works, it's a bit of an either/or ... rather than a somewhere in between which was what the separate rates is about in the 1st place.
