Wester, I encourage you to consider bookmarking the books that you physically have on hand. Besides solving the issue that you've asked about, it would also allow you to begin other lists (bookmarks) -- wishlists, books available in your local library, books available from friends (to view or borrow), books on a topic you want to explore, etc. Currently, because there's no way to tag a number of books and apply a bookmark to them all at once, it will take a little bit of time and effort on your part to compile the list of your actual holdings. The payoff is being able to build other kinds of lists (bookmarks) while having a way to limit recipe searches to books on hand when you need to. The bookmark I use for this is 'kitchen shelf', and it includes magazines as well as cookbooks.
If your books are in different locations in the house, it might make sense to have an overall 'Have' or 'Here' or 'on hand' bookmark (for purposes of recipe searching), and then an additional one for the room/location. It's worth giving a little bit of thought to how you want to approach it before bookmarking a substantial number of books, because the bookmark names can't be edited once created, only deleted. They only display alphabetically, also.
In the future, if/when there are the development resources to make it happen, being able to include or exclude any number of bookmarks that a member specifies (using checkboxes) will be a great step forward. The more kinds of bookmarks you have at that point, the more power will be unleashed by that feature.
Related features to hope for are mass tagging/bookmarking, and editable bookmark names.
The quickest way to that bright future is to make effective use of EYB and then let cooking friends know about it. Hope you'll find it increasingly useful.