Adding a second drive to Optiplex 7090 Ultra

I have one of the new Optiplex all-in-one where the computer module fits in the monitor stand.  It came with a 512Gb M2 short drive as the main OS drive in the slot I hoped to be able to use for an extra drive some form of hard drive bracket on the reverse side which does not allow access to any of the slots on that side to fit an extra drive. I have yet to find out how I can fit an extra ssd drive of any sort, M2 or other type of SSD. Putting my service tag into the support site shows a different type of Optiplex UFF and drives that I cannot see how to fit without changing the case cover of the module.  Emails to technical support have not given me a sensible answer. Can anyone help?

I have included images of both side as they were when delivered.