The best way would be to setup a tftp server that each of the units could hit, which would have the cpconf and firmware file loaded on it. Some interaction with the Portserver would still be necessary to give it an IP and gateway address, as well as tell it which firmware and config files to download.
This would only work for models of the same type, for instance you wouldn't be able to use firmware/config for a TS16 on a TS4 or Digi One, only on other TS16's.
Here are a couple articles to help get you started:
http://support.digi.com/support/kbase/ta.php/kbase_any/ps2/kbase_any/20020806133001/
ftp://support.digi.com/support/techsupport/hardware/portserver/Portserver_Upgrade.htm
ftp://support.digi.com/support/techsupport/hardware/portserver/tftpcpconf.html