Not sure but here is a W.A.G.
What if mingetty was run only on tty 12?
Found in inittab:
# Run gettys in standard runlevels
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6
Maybe change to:
# Run gettys in standard runlevels
12:2345:respawn:/sbin/mingetty tty12
This is completely untested!!