I'm afraid you do have to have a recipe on your Bookshelf in order to bookmark it. Bookmarks are a function of your Bookshelf, not the Library. You can add notes and photos for recipes not on your Bookshelf though. One way around the issue of bookmarking is to see if you can find the recipe online - either email us or add a note with the link and I will then add the online link to the recipe. You can then add the recipe to your Bookshelf. Just a warning though, we cannot always add links, especially for new cookbooks, as publishers have imposed limits on how many links we can add.
Another option is to add the recipe as a personal recipe. This is espcially useful if you copied the recipe from the borrowed book so now have the recipe available and want it in your searches. Once the recipe is on your Bookshelf you can bookmark it. Though any notes or photos you add to that recipe will not be visible to any other members, so maybe add in both places if you can.