Facebook Graph API - Post on Group wall as Group

Question

I am trying to post to Facebook Group Wall via Graph API. When i make the post, owner of the post is set as my personal id. Would someone know how to make Group has the owner of the post. Below is my current code:

form_fields = {
        "message": 'This is message title',
        "link": 'http://facebook.com',
        "name": 'This is message title',
        "access_token": 'token here'
    }
form_fields['description'] = 'This is message body'
form_data = urllib.urlencode(form_fields)
response = urlfetch.fetch(  url="https://graph.facebook.com/%s/feed" % group_id,
                                    payload=form_data,
                                    method=urlfetch.POST,
                                    deadline=10
                                )