You could try and form some cardboard around the comb binding (like cut part of a cereal box down (the side edge) and shape it around it. And also put it in a padded envelope.

A box really would be best.  Cut down/recycle an old one.

I shipped a few spiral bound cookbooks and I added filler (bubble wrap, crumbled paper without ink, etc.) to build the flat part of the book up to the height of the spirals, the I covered it in plastic, added a piece of cardboard on either side to completely cover the front and back of the book, taped the cardboard in place, and then put it in a mailer. I agree a box would have been better but I couldn't find boxes the right size. Something I now think about before I list an oversized or odd sized book.

Box.  That type of binding could easily be damaged by Media Maul.

I successfully shipped a book with spiral binding by inserting some tissue paper down the center of the binding.  It would depend on how much space there is and if you can get tissue paper into the gap between binding and pages.  I then did something similar to what Lsressler did.  Definitely build it up with bubble wrap and use cardboard to shield it.  Good luck!