The Gentoo Printing Guide does not document a mandatory kernel option needed to use a parallel port printer and CUPS. With kernel 2.6.27-gentoo-r7 the .config option PRINTER=y or PRINTER=m is needed. It is found in menuconfig menu under "Device Drivers" -> "Character Devices" -> "Parallel printer support". Reproducible: Always
Im just plain wrong on this, sorry for the noise. This option is clearly already there.