I think you can get though the breast bone with a good chef's knife and a mallot or hammer. Remove the back bone first with a sharp knife or kitchen shears by cutting along both sides. Save this for stock. Then place your knife on the inside of the turkey against the widest part of the breast bone toward the neck, and either pound with your hand or chop with a cleaver, or use a mallot or hammer, and "score" through the bone. Then try to "flatten" and break the breast by pushing on the two sides. Continue to cut through with a knife. The breast bone is much softer than beef bones, and should be able to be split without major saws. The point is... to spatchcock it, and place each half on it's own rack. However you get there, getting 2 halves, if you need to go all caveman on it, is fine.