I think it is a good idea to let the restricted manager install the firmware. It could use the script which giner has posted and the download could be triggered either by the installation of foo2zjs or by plugging a LaserJet 1000/1005/1018/1020 to the USB, using a HAL script. The printers are USB-only so triggering the firmware installtion by plugging the printer is always possible.
I think it is a good idea to let the restricted manager install the firmware. It could use the script which giner has posted and the download could be triggered either by the installation of foo2zjs or by plugging a LaserJet 1000/1005/1018/1020 to the USB, using a HAL script. The printers are USB-only so triggering the firmware installtion by plugging the printer is always possible.