Extension 'Export to PDF in CMYK'
The Extension 'Export to PDF in CMYK' generates a vectorial file in PDF format using the CMYK color system. The resulting elements of the PDF file maintain the exact values applied in the art on Inkscape, different of the default export made by Inkscape that uses Cairo and applyes just RGB values to the elements. The extension uses the software UniConvertor to generate the PDF file. The extension can be inproved, but it already gives acceptable results.
Copy the two files to the folder /usr/share/inkscape/extensions