[ubuntu] Serial console with preseed on 12.10

I have a pile of servers that I need to install using only the serial console for display. I have a preseed file that is mostly working however one thing I can't seem to figure out how to do is enable the serial console via the preseed file during install. Any ideas on how to do it? The serial console help file does not mention how to go about doing this either.

https://help.ubuntu.com/community/SerialConsoleHowto