I did this a while ago. Ruined a magpul follower and went to a green follower. Shaped it so it would fit into the 20 round magazine body.
20 round floorplates use a flat piece of spring steel tacked into the mag body to hook into the floorplate, so if you ruin it, you need to run 30 round magazine floorplates.
The magazine works well, but not any more of an improvement over the old black or alloy followers.
http://img186.imageshack.us/img186/9642/grn20b.jpg
http://img833.imageshack.us/img833/3264/grn20a.jpg