Finish Line makes Extreme Fluoro grease which is repackaged DuPont Krytox, in a needle syringe applicator which fits nicely in the end of cable housing. This is basically pure PTFE dry grease so shouldn't attract dirt.

I only rarely use it for lubing cables, however Krytox is about the best stuff you can get for lubing o-rings and threads in some applications such as bike lights and handheld flashlights, so I keep a syringe around. It's the only way I've found to get it in small quantities.