That books integration looks fascinating (though the previews don’t seem to work, I just get an empty lightbox). What I had in mind was oneboxing the preview, but this might also work (when it works), maybe even better.
I will have to look into that source code later to see what in those 1383 lines is relevant here (I am not a programmer).
Are you saying that the whole integration is done only via JS, no discourse plugin?