ok, so I have this working 
you will need a new version of mother to be able to use the sdcard for patches, which I now have, and will release a beta ‘shortly’… also the instructions below are for those happy with linux, Id hope later we will be able to script these for everyone, to just fire off from the organelle lcd (like the upgrading of OS)
steps required:
a) get a bigger SD card, make sure its fast - Ive used a 32GB I had lying around
(actually smaller are usually faster, so ideally use the smallest that has enough space for you - remember organelle os is currently using 4gb, so an 8gb card will mean you have 4gb for patches/samples etc)
b) install the Organelle image on this card, I use DD, but there are lots of tools that can do this, as @oweno mentioned
c) take the 4gb card out from your organelle and insert your new one
(this is cool, means you have a backup if this goes wrong 
)
d) power up organelle, all should be as before.
e) you now need to log into organelle using ssh , then do the following
run disk to create a new primary partition, you can accept the defaults
fdisk /dev/mmcblk0
n
p
w
then you need to reboot
reboot
you now need to create a filesystem on the new partition
mkfs.ext4 /dev/mmcblk0p2
now we need to check it works, so we need to create a mount point, which means we need to write to the main disk
by mounting it… then we mount it to check it works
~/scripts/remount-rw.sh
mkdir /sdcard
mount /dev/mmcblk0p2 /sdcard
ok, you can go to the /sdcard and check you can write files there ok
now we want it to mount automatically on startup, so alter fstab
vi /etc/fstab
/dev/mmcblk0p2 /sdcard ext4 defaults,noatime 0 0
thats it reboot organelle, copy over your patches from your usb card,
then assuming your using my new mother, you can shutdown your organelle, remove the usbcard, and now organelle will use your sdcard
dev note:.
we could script the above, so could be done without logging into organelle
@oweno - I think arch linux is using < ~2gb , so perhaps, we could even repartition the supplied sdcard, to give 2gb for patches? … this would be cool, so you know everyone is using sdcard… not sure how practical this is!?
Ive changed ‘mother’, so that if /usbdrive/Patches is present, it will use that, if not then it will look for /sdcard/Patches… if thats not present it will assume /usbdrive/Patches (i.e. to give current behaviour)
this works well I think, since it means you can use the usb drive to ‘override’ the internal patches
Im also planning to do the same behaviour for system/scripts e.g. priority is /usbdrive/system -> /sdcard/system -> /root.