the differences to regular trunk version compile are:

CMDLINE = "mem=200M console=ttyS2,115200n8 console=ttyGS0 musb_hdrc.mode_default=2 androidboot.console=ttyGS0 root=/dev/sda2 rw media=/dev/sda1 init=/init android omapfb.vram=7372800 vram=7372800 extrabaud=1000000"

in the init script in initramfs:

install_g_serial()
{
        $INSMOD /lib/modules/$KERNEL_VERSION/kernel/drivers/usb/musb/musb_hdrc.ko mode_default=2
        $INSMOD /lib/modules/$KERNEL_VERSION/kernel/drivers/usb/gadget/g_serial.ko n_ports=3
        mknod /dev/ttyGS0 c 253 0
        mknod /dev/ttyGS1 c 253 1
        mknod /dev/ttyGS2 c 253 2
        cat /proc/kmsg >/dev/ttyGS2 &
}

gets called after 'display_banner'

that's all folks!

PS: if you're on Windows look at this: http://www.kernel.org/doc/Documentation/usb/gadget_serial.txt
    Specifically 'Installing the Windows Host ACM Driver'