You can run the following command as SYSTEM, "dsregcmd /join". To run it on a remote computer you can run it with psexec or stay in powershell and run Invoke-CommandAs. It is compatible with Powershell 3 and above.
To install Invoke-CommandAs:
- Install-PackageProvider -Name NuGet -Force
- Install-Module Invoke-CommandAs -Confirm:$False -Force
To hybrid join an existing Active Directory joined machine:
- Install Invoke-CommandAs on local machine
- Run Invoke-CommandAs -ComputerName computernamegoeshere -ScriptBlock { "dsregcmd /join"} -AsSystem -RunElevated