Blake,
You can put your drip tip on your cartomizer (just remove the plug and replace with the drip tip ) and then when your carto is running low, drip down the inside edge of the drip tip to top off the carto.
Ooops, was on page 1 thought I was on page 2 and missed the above posts.
Don't drip directly through the drip tip into the carto; drip so the juice will run down the inside of the drip tip. Or as Day points out, just pull the drip tip off and top off.