No rack is really safe to mount to carbon.... (unless the frame specifically has bosses for that purpose). It's not just about weight. If any of your attachment points rubs through the finish and scores the carbon itself you've hurt the integrity of the material. Ruin the seat post and yes you could get a new one. Ruin the rear stays of the bike and you'd need a new bike. Since your Ruby wasn't made to accept a rack any mounting that you would do would have to be jury-rigged and even more likely to cause damage to the frame. It's not a gamble that I'd want to take.