Redirect console to a serial port
You could launch getty once you've booted to get a serial connection to your system. Note that this will not give you the default outputs typically seen with your console (Kernel Panics and other verbosities typically seen in console but not in normal terminals). But if you are just looking to get a login via serial after boot this should work.
/sbin/agetty -L 115200 ttyS2 vt100
That should connect to /dev/ttyS2
at 115200
baud and emulate a vt100
terminal.