Disable unused console (tty) when using Upstart init daemon

There are not /etc/inittab anymore, but /etc/init/ttyN.conf (N from 1 to 6). Just comment out the last line in each file you desire. For example (in /etc/init):

$ cat tty1.conf

# tty1 - getty
#
# This service maintains a getty on tty1 from the point the system is
# started until it is shut down again.

start on stopped rc RUNLEVEL=[2345]
stop on runlevel [!2345]

respawn

exec /sbin/getty -8 38400 tty1

$ cat tty1.conf | wc -l

10

$ sed -i '10 s/^/#/' tty{2,3,4,5,6}.conf

Please tell me other command lines to do the last job.
P.S. in an Ubuntu box Ctrl+Alt+Backspace now is Right Alt (Alt Gr) + Print Screen + k.