So I decided to do this the powershell way. Turns out it was just 2 really simple commands:
New-Item HKLM:\SOFTWARE\Policies\Microsoft\Office\15.0\Lync -Force
New-ItemProperty HKLM:\SOFTWARE\Policies\Microsoft\Office\15.0\Lync -Name DisableServerCheck -Type DWord -Value 1
Do remember that you have to run PowerShell with Administrator rights.
UPDATE: Now that skype for business 2016 is launched, it's time to update the script a little. Use this one below instead.
New-Item HKLM:\SOFTWARE\Policies\Microsoft\Office\16.0\Lync -Force
New-ItemProperty HKLM:\SOFTWARE\Policies\Microsoft\Office\16.0\Lync -Name DisableServerCheck -Type DWord -Value 1