All you'll need for this, is whatever grit sandpaper you want to use, some quality tape, and a sanding drum for your dremel.
Start off by getting your sanding drum, and screwing the screw all the way out, thinning out the drum.
Next, grab your tape and get a strip that is the right size for the drum, I'm using some good quality duct tape.

Now wrap the tape tightly around the drum, sticky side out.

Now cut off a strip of sandpaper the same width as your tape.

And wrap it around, in the same direction you wrapped the tape.

Trim off any excess as close as possible to the other side of the sandpaper, you want no tape showing, but you also don't want any sandpaper flapping about.

Sorry, blurry
Ok now tighten down the screw carefully, you don't want to stretch the tape and thereby widening the gap in the sandpaper.
Ok last step, when you put it in the dremel, make sure that it's going to spin in the correct direction. You're likely to have a little bit on the edge that wants to either come up, or overlaps a little. This fine, but make sure the direction the dremel is spinning will make the flap not catch.
Now words of warning. Wear your saftey glasses. Don't be dumb.
Ok, I have now made two of these, a 1000 grit, and a 2000 grit, and I'm seriously happy with how they turned out. I've spent some good time with both and have had no issues. That in mind, I generally keep the dremel at a much lower speed with these drums on it, and tend to be very light handed while sanding. I wet sanded the entire time with the 2000 grit, and other than randomly getting hit in the face with sprinkles of water, there were no issues. I dipped the pick into the water, not the dremel though. (I really wish I didn't have to say that.)