There is even a _very_ old ticket of mine that states it would be nice to have offline installability, but the most we came to getting it done was l3mce's work with the live DVD.
But, if all you want is upgrading your package pluto-dcerouter, go into the commandline on your core, and edit line 104 of /var/lib/dpkg/info/pluto-dcerouter.postinst
/usr/pluto/bin/WebDB_GetIR.sh 0 "$Template"
/usr/pluto/bin/WebDB_GetIR.sh 0 "$Template" || :
and run apt-get -f install.
This will get your package installed, but won't install the IR code updates. If you have the IR codes on another system, you can use the DeviceTemplate exporter that is somewhere on the forum to export the IR codes into a file on your other system, and follow the instruction to import them to your new system.