I use a modified version of this, and its so ridiculously easy I couldn't believe it. I got an Oral-B rotary brush (I looked at all the ones at the grocery store and grabbed this one because the bottom section looked like it could easily be snapped out leaving just the top rotary part) for $5.99. (I even sat there in the store feeling silly after turning them all on to make sure they spun instead of going back and forth.) I went over to the aisle with the lightbulbs and glue and minor sewing stuff and found some self-adhesive velcro squares. Cost me $3.50 for the velcro.
I went home and started playing- I took out the brush from the package, snapped out the lower section of the brush head (it was cake) and snipped a bit of velcro off one of the squares (approximately a half inch teensy piece of velcro.) I grabbed a pair of scissors and sheared the bristles down on the brush head, trying to keep the remaining bristles as level as possible. Then I took the backing off of the rough side of the velcro and stuck it to the spinning brush head.
I took my scissors again and adhered a soft piece of velcro onto a small circle of my 400-grit wet/dry sandpaper. Stuck it to the end of the brush, and viola- instant hand sander.
I even made myself a "sanding board" with replacement heads velcroed to it with everything labeled from 400 to 3000 grits.
I'll never have to replace the actual brush head unless it breaks, or buy extras for different grits, and the velcro has been holding up under pretty extreme circumstances. Whenever one of the sandpaper pieces wears out I just grab the velcro and my sandpaper sheets and make another "sanding wheel."