Is that UPS wall mountable?
If so, with all of those holes on the left side (facing desk) you should be able to hang the UPS there. Or on the back even.
If not wall mountable, you may still be able to install a simple wire rack in either of the same locations to support the UPS. Just do not cut off the airflows.
I have done such things several times so when the desk or cabinet is wheeled out for access the UPS comes along with only its power supply cord trailing along. Very nice to have the UPS up out of the way.