More code that I've hacked together in VBScript to get the username used to start a particular service on my system:
Dim objWMIService, objService, strServiceStartName
Dim colListOfServices, strService
Set objWMIService = GetObject("winmgmts:{impersonationLevel=impersonate}!\\.\root\cimv2")
Set colListOfServices = objWMIService.ExecQuery ("Select * from Win32_Service where name = 'MSSQLSERVER'")
For Each objService in colListOfServices
strServiceStartName = Trim(objService.StartName)
Next
wscript.echo strServiceStartName