I just bought a couple of these and I have access to a lathe, but I think in order to hold on to these "real good" I'm going to have to buy the "Back Pad" that these bristle disks screw to (shown below).
http://www.sculpt.com/catalog_98/abrasives/3m_finishing.htm
First It would only make sence to snip off the paddles from the original impeller.
Put the back pad in the lathe, screw on the bristle pad, and begin removing the outer ring of bristles. I'm thinking than I can then chuck the thing gently on its outer perimeter to drill the center hole, but I would prefer to start drilling a guide hole while it is still in the lathe.
The tricky part is "how to shorten the bristles"? I'm thinking that the only way to make them all even and shorter is to wear the down. One could use a small steel plate, weld a rod coming out of the plate. The rod can be perfectly alligned using a drill press to hold the rod. Once this "wear plate" is made it can be put in the lathe and use it to even wear down the bristles. Just turn on the lathe, bring the plate in on the bristles and lock it in place. I amagine after a few minutes you can bring the plate in a little more.
The only thing that I'm a little worried about is how flexible it is compared to the Euro Reef Needle Impeller. Euro Reefs' is tough like HDPE (High Density Poly Ethylene) but still flexible.
So the green ones are not as stiff? Thats strange, they are listed as "coarse" and the yellow ones are listed as "medium". The yellow ones are the only ones in stock at my local NAPA.
If this works well I'll make another one but show some pics.
THIS WILL WORK