matt,
I used the Neeyer SATA to USB Cable adapter from Amazon to install a 3rd 8TB Samsung SATA SSD. Seems to work OK - no idea of speed but it seems adequate for backups which is how I use it.
There's a USB port just to the left of the two SATA ports in the 7,1
Tom
PS: the wire length was tight - after a little bit of wiggling, everything seemed to fit fine.