Upper River Shops

From Fallen London Wiki

With the release of Ealing Gardens, we now have our first shops outside London, not counting the Iron Republic's cameo. The problem is that these shops let us sell items for Hinterland Scrip instead of echoes—but our templates currently only allow for items bought or sold in a single location. How can we adjust them to handle buying and selling in multiple locations, in multiple currencies, without causing problems with the current use?