Based on these instructions:
http://ubermix.org/download.htmlWe did the following, on Linux:
1- Copy one of the USB drives that have the updated image to a file, called custom_ubermix.img:
sudo dd if=/dev/sdb of=custom_ubermix.img bs=1M
Be patient, there is no progress information.
Note: Use the instructions in the link above to find out if your drive is /dev/sdb or something else.
2- Unplug the original USB drive, and plug in a blank one (or one that you want to overwrite).
3- sudo umount /dev/sdb
4- sudo dd if=custom_ubermix.img of=/dev/sdb bs=1M
In this last step, be patient, because there is no progress information. It should take around 5 to 10 minutes, depending on the size of the image, and the speed of your USB drives and USB ports.
I hope it's clear. Using the Windows based tool in the link above, you should also be able to do a similar process of copying an existing USB drive to an image file, and then use that to create copies.