You mention that you also want to automate startup. One way of achieving this would be to manually add an PASSWORDS_listener_name entry to listener.ora, specfiying a password in cleartext. Do not use the netmgr or the set_password command. I think this script should work (not got access to my 9iR2 ServiceGuard package control script at the moment):
$ORACLE_HOME/bin/lsnrctl << !
set current_listener listner_name
set password password
Naturally you should make sure that your listener.ora file and your shell script are fully locked down at the OS level permissions wise and that they stay that way.