set fastCgi with appcmd

The official FastCgi section says:

You can configure the <fastCgi> element at the server level in the ApplicationHost.config file or at the site level, at the application level, or at the directory level in a Web.config file.

However this is not by default, since applicationHost.config has pre-defined:

        <sectionGroup name="system.webServer">
           ...
            <section name="fastCgi" allowDefinition="AppHostOnly" overrideModeDefault="Deny" />
		   ...
		</sectionGroup>

Thereby if type this command:

appcmd set config mainsite /section:fastCgi /+"[fullPath='d:\php\php-cgi.exe',arguments='-d open_basedir="d:\mainsite"']"

It just throw such error:

ERROR ( message:New application object missing required attributes. This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false".. )

NOTE: the parameter should be quoted if contains any space!! That means , you can't even type as :

C:\Windows\System32\inetsrv>appcmd set config mainsite /section:fastCgi /+[fullPath='d:\php\php-cgi.exe', activityTimeout='500']

beause a space is padded in between "..-cgi.exe'," and "activityTimeout". Typing as this causes such error:

Failed to process input: The parameter 'activityTimeout='500']' must begin with a / or - (HRESULT=80070057).

Nonsense.