The answer here wasn't very elegant (in my mind at least) but here is what I did to achieve the desired result:
- Create the VM as usual (specifying the admin user during setup)
- Create a new (non-admin) user and give them RDP access
- Log in as the non-admin user
- Install all the necessary software
- Log in as the admin user, change the permissions for any files that were causing an issue to be readable by the non-admin user
- Run sysprep as the admin and complete the process as detailed elsewhere
This gave me an image that I was able to provision VMs from. When creating the VM I specified the admin user to be created (but then never needed to login as the admin, as I would just login as my non-admin user that was created before). All profile settings for the non-admin user are preserved.
Hope this helps anyone else facing the same issue.