I have never tried running cups on my router but Optware has cups.
From ipkg list
cups - 1.4.6-1 - Common Unix Printing System
cups-dev - 1.4.6-1 - Development files for CUPS
cups-doc - 1.4.6-1 - Common Unix Printing System documentation.
cups-driver-gutenprint - 5.2.6-1 - CUPS driver from Gutenprint.
cups-locale-da - 1.4.6-1 - CUPS documentation, template and locale files for da
cups-locale-de - 1.4.6-1 - CUPS documentation, template and locale files for de
cups-locale-es - 1.4.6-1 - CUPS documentation, template and locale files for es
cups-locale-eu - 1.4.6-1 - CUPS documentation, template and locale files for eu
cups-locale-fi - 1.4.6-1 - CUPS documentation, template and locale files for fi
cups-locale-fr - 1.4.6-1 - CUPS documentation, template and locale files for fr
cups-locale-id - 1.4.6-1 - CUPS documentation, template and locale files for id
cups-locale-it - 1.4.6-1 - CUPS documentation, template and locale files for it
cups-locale-ja - 1.4.6-1 - CUPS documentation, template and locale files for ja
cups-locale-ko - 1.4.6-1 - CUPS documentation, template and locale files for ko
cups-locale-nl - 1.4.6-1 - CUPS documentation, template and locale files for nl
cups-locale-no - 1.4.6-1 - CUPS documentation, template and locale files for no
cups-locale-pl - 1.4.6-1 - CUPS documentation, template and locale files for pl
cups-locale-pt - 1.4.6-1 - CUPS documentation, template and locale files for pt
cups-locale-pt-br - 1.4.6-1 - CUPS documentation, template and locale files for pt-br
cups-locale-ru - 1.4.6-1 - CUPS documentation, template and locale files for ru
cups-locale-sv - 1.4.6-1 - CUPS documentation, template and locale files for sv
cups-locale-zh - 1.4.6-1 - CUPS documentation, template and locale files for zh
cups-locale-zh-tw - 1.4.6-1 - CUPS documentation, template and locale files for zh-tw
cups-pdf - 2.5.1-1 - CUPS-PDF provides a PDF Writer backend to CUPS. This can be used as a virtual printer in a paperless network.