I researched this rather extensively with some outside colleagues recently. Although it is uncommon practice currently (for providers & hospitals), it is a separate record--not done by the physician, but by the asst. surg (whomever that may be). CPT Asst. 1992 (I believe, and thank you, Mr. Bush for helping with that) says something to that effect.
I say an addendum to the surgeon's record may suffice, as long as it also bears the surgeon's signature as well.
Good luck.