Edit the tty configuration in /etc/init/tty*.conf
with a shellscript as a parameter :
(...)
exec /sbin/getty -n -l theInputScript.sh -8 38400 tty1
(...)
This is assuming that we're editing tty1 and the script that reads input is theInputScript.sh.
A word of warning this script is run as root, so when you are inputing stuff to it you have root priviliges. Also append a path to the location of the script.
Important: the script when it finishes, has to invoke the /sbin/login otherwise you wont be able to login in the terminal.