Check this out, I saw this in a recent AMCN, Awesome Discs in Melb. do this mod to standard round discs, they charge from $120 per disc.
I thought "I'm a bit of a tightarse but I'm clever enough to do that myself" so I got an old butter knife out of the kitchen draw & started carving.
I can do these for about $75 per disc if anyone's interested.