How can I fix my squeaking ebrake?

[RallyEclipse98]

When I set my ebrake, I get a sqeaking sound from the passenger rear of the car. Sounds like the cable is just super dry. I jacked the car up to lube the cable. The cable is in a closed system so I couldn't spray any PB blaster anywhere to solve the issue. But I was just watching Mighty Car Mods. I noticed on the back of some disc brakes, there was a little observation window cut into the dust shield. Is that how I'm supposed to lube the ebrake? Just stick the straw up in there and spray away? Or is this even possible?

I know this is a nit-picky post but I just want my DSM to be perfect.