Using the Reading List plugin I add all new books to a 'New' Reading List. This is then automatically synced with my device(s) when they are connected (and the list then cleared).
https://www.mobileread.com/forums/sho...d.php?t=134856
I also use this plugin to automatically add a 'OnDevice' tag for the books currently on my ereader so I can easily see which books I have on it even when it is not connected.