Interesting code chunk from /etc/init.d/bootopts.sh:
home=*)
# Check for a specified home partition (home=*) and check for
# user home dir. Note: home=usb is a shorter and easier way to
# have home=/dev/sda1.
DEVICE=${opt#home=}
[ "$DEVICE" = "usb" ] && DEVICE="$(usb_device)1"
echo "Home has been specified to $DEVICE..."
DEVID=$(/sbin/blkid | sed 'p;s/"//g' | fgrep "$DEVICE" | sed 's/:.*//;q')
if [ -z "$DEVID" ]; then
USBDELAY=$(cat /sys/module/usb_storage/parameters/delay_use)
USBDELAY=$((2+$USBDELAY))
echo "Sleeping $USBDELAY s to let the kernel detect the device... "
sleep $USBDELAY
fi
Appears that this is not enough?