Get there: More > Tools > Catalog > Quick Spine Label Creator
This tool does not use the label layouts or templates, it simply prints a spine label in the first spot on the label sheet.
Define the fields you want to print on the spine label in the SpineLabelFormat system preference
Format your label printing by editing spinelabel.css found in koha-tmpl/intranet-tmpl/prog/en/css/
To use this tool you simply need the barcode for the book you'd like to print the spine label for.