You can do nearly anything in nearly every language - it's just a question of whether or not it's practical...
In order to do what you're asking, you'd need to at least partially reverse engineer some parts of the game, in order to add a new section on the starting screen for the new mode. The actual functioning of searching a folder is easy to implement in almost any language. One of the exceptions to this unfortunately is Lionhead's challenge language used in the scripting.
You should be able to specify folders outside of the usual working directory using chl language easily enough when loading a
known map for example, but as far as I can tell it offers no means of searching a directory and updating a list in-game, without recompiling the script. You could make an automatic script generator that does this whenever you execute it (you certainly wouldn't need C++ for that though), but then you'd have to run the program, start BW, start a new game, load up the map-loading map, and then load the map you wanted; as opposed to changing one word in map.txt, then loading the game and starting a new game.
Large Hadron Collider - because fleshlites are for wusses