You can make a list in your extended profile. But you can't register them (give them a BCID number) if they are not yours to write in or sticker on.
It may help to keep in mind that BookCrossing is more about the book as an object, the physical book, than about the book as a text. If you do not own the physical book, you cannot register it on BookCrossing. A good option for making a record of books that you have read is Goodreads.com. That site is all about the book as a text and has nice features especially for that.