Aaaaah, the cable-splitter fits between the brake arms, ay? Ingenious, and if I'd thought about I'd've realised that's the only piece of exposed inner cable so the only place it can go.
Well, this suggestion might be a bit controversial: do you split the frame that often? Do you really need a cable splitter? Could you not just unscrew the aforementioned cable clamp bolt if you do need to split the frame...? I know, I know, it's a cool gizmo and I would hate to see it go too!