Now this is a neat idea despite not giving a damn about Nintendogs. Slot-2 cheat devices dedicated to single games.
This idea is the first thing that came to mind after being disappointed in having beat Mario Kart DS in less than a single day. Ninetndo SO could have used slot-2 for track expansion packs to keep the game fresh longer but typical Ninendo they don't seem to ever go all the way and miss great opportunity's so often.
Can't find any threads about this particular issue on GBAtemp or the wider intarwebz. Saw one video on YouTube that seemed relevant, but it was some dude with the same issue, no solutions offered in the comments. :/