Depends on how much effort you're willing to put into the project. Techically you could solder some wires to the LCD driver's output and then work on converting that, but I don't see why you wouldn't just use the output that's on the console itself.

 

There has been talk of it here and there from the 3ds capture forums, but nothing has come of it yet. Really the only use for it is showing a video where the GP and TV have entirely different screens and you want to show them simultaneously.