I have never tried this before, but am interested in doing so. I know that you can copy and push some settings out via the web interface, but you still need to manually configure some things.
What type of USB drive(s) are you trying to use? Did you try a USB 2.0 drive? They should be backwards compatible, but I have seen USB 3.0 drives not work with some devices.
Also, how is your drive formatted? It may only recognize certain file types like fat/fat32. There also could be issues with using a very large drive, so you could try something smaller.
Howdy friend! How's life since leaving the old stomping grounds?
As far as the USB question, I have tried drives of multiple sizes and brands (It's amazing what can be accumulated from what students leave behind and never come back for!) I have tried as small as 256MB and up to 2GB, used off-brand, Sandisk, PNY, Crucial, etc. All were cleaned and formatted in FAT or FAT32, sometimes tried both. The end result was still the same. I just bit the bullet and started configuring them manually and I am nearly finished with them. Once I am done, my lab printers will be setup for secure release and a single print group, which will make things nice here for the students, and cut down on wasted paper!