If you have one of these laying around, they greatly assist in the whole carto-plug, pulling/replacing process.
I put the point in just enough to hook the underside of the plug, then twist it out. The plug stays put on the hook while I fill the carto, then I just pick it up with my index finger holding the plug on the hook, put the hook point in the mouth of the carto, and slide the plug into position. When I don't use this, the little plugs have a tendency to roll or bounce off into oblivion.
It came with a dull hook and a mirror as part of a Gum brand dental care kit I got at the supermarket for something like $5. I use the other tools, but I'm WAY to clumsy to be sticking something this sharp in my own mouth.