I'm not aware of any way to do it in the Book Module. If you have Photoshop, and you have the same fonts available to both applications, then you can see previews of most of the fonts in the font pull-down menu of the Photoshop text tool. Not directly what you asked, but it could be a workaround (and easier than trying a sample of each font).
Be aware that Lightroom modules seem very picky about which fonts they will use - many are incompatible - they either do not show at all in Lightroom, or they cause errors and lock-up problems. eg.FONT PROBLEMS (RHC)