IF you want to see what it would be like to scale the screen horizontally, try the "software renderer" version of v0.4a which doesn't take advantage of the DS's 2D hardware to perform fast drawing operations, like all other versions of jEnesisDS do. Somewhat playable with enough frameskip, but unless a game absolutely needs it, I'd compromise with just vertical scaling.
https://gbatemp.net/threads/jenesisds-v0-4a-released.55439/
https://gbatemp.net/threads/jenesisds-v0-4a-released.55439/