That video is pretty spot on although you really don't need to place filler back into the Carto to prevent any leaking from the bottom of the Cartomizer.
The Metal Air Wick Tube extends up about a 1/2 inch from the Carto Base. Every Carto has the following: An outer layer of Polyfill, Wicking Material, then the Wick Tube itself. The Wicking material already coats the bottom of the Carto base....so wicking is not an issue since you are just removing the Polyfill.
Let me show you what I mean:
Vapor4life Tips, Tricks & Fixes for Cartomizers - YouTube (3:40 mark)
Now, keep in mind....you are dripping...so you don't want put anything more than just a few 2-3 drops in at a time, then vape them down. Those 2-3 drops will give you about 8-12 good draws, depending on how long and hard you draw. I generally vape with long slow measured draw for about 7-8 seconds.
Anything more then 2-3 drops will lead to over-saturating of the wicking material which may lead to poor or no performance. Should this happen, toss the Carto on a Passthrough, the extra voltage will bring it back to life by steaming off the excess juice. It will also make for a great vape hit so-to-speak.
Now I have never done this with 100% VG juices so I don't know if the results are the same as some juices can be very thick compared to others. I would guess that everything would be the same other than you might be able to get a few more draws since VG generally last longer. That is to say it doesn't steam/vape out as quickly as a PG/VG blend.