I have a licence and administrator access to the SharePoint servers.
Is it possible to automate the import of the licence file using either powershell, or using the forms equivalent of nwadmin.exe?
I will answer my own question for others benefit!
Once you install the NintexForms2013Core.wsp, and run a SharePoint management console, the Update-NFLicense command is available, that takes a filePath parameter for the licence file. This can be run remotely, via ssh etc.