The article Programmatically updating local policy in Windows describes a .NET library that can assist with this problem.
If you do not wish to write a .net program, the simplest solution would be to create a AutoHotkey macro, possibly compiled to an .exe, that will do the GUI manipulations that create that group policy.
If you are using Windows 8 or Server 2012, the configuration of QoS is possible via PowerShell:
Network Quality of Service (QoS) Cmdlets in Windows PowerShell.