Nah, you can grind a flat onto one edge and run the brake pads at an angle (I've seen it done)
Basically, a d521 is great for street. Maybe a wider "cheese" rim for natural.
My mech is currently held like this. The round bit under the tape is a section of a syringe and this seems to work ok (touch wood)
Could someone please explain how i can fix it using a gear cable in a bit more detail?