This is second hand info for the most part (casual conversation with other travelers): Apparently, there are offices around that are the equivalent of a notary public in the US that will do this for a small fee.

Now the first-hand info: The only thing I have ever done in Rio is keep a NON-certified copy of the photo page and Brasil visa page of my passport. I've asked in the hotels before and they have told me that is good enough ... but I have heard that the certification is technically required and that some folks have been given a hard time before. After over a dozen trips to Rio no one has ever asked me for my passport (after clearing at the airport of course).

Of course your real passport should be in the hotel safe at all times locked up ... IMO anyway.