I did this by just manually downloading the nupkg package from the powershell gallery. Extracting with 7zip and copying to my modules folder and my IIS folder.
Alternatively if you dont want to mess about with 7zip, just use install-module on a PC you do have connectivity from. Then copy the module folder for UD under: ‘C:\Program Files\WindowsPowerShell\Modules’ from you machine, to the offline machine, in the same location.