Change User Agent and Headers in pyWebkitGTK?

I've read the suggestions for making your own data handler, for example:

web_view.connect('resource-request-starting', resource_cb)
def resource_cb(view, frame, resource, request, response):
    print request.get_uri()
    #get data using ur开发者_如何学运维llib with different user-agent...
    request.set_uri('data:....')

(from http://code.google.com/p/pywebkitgtk/wiki/HowDoI)

will let you download using custom header/useragent. However, sometimes it will complain if set_uri is given string with null-char, or it will give an error like "** Message: console message: (http://url) @linenumber: SECURITY_ERR: DOM Exception 18: An attempt was made to break through the security policy of the user agent."

Is there a better way to set a browser useragent for pygtk code? This says you can add/remove/replace headers using SoupMessage, however that documentation is missing...

This code sets a special user-agent:

http://nullege.com/codes/show/src%40p%40r%40PrisPy-HEAD%40PrisPy.py/33/webkit.WebView/python

webkit.WebSettings() allows user-agent switching, and a few other settings, but it seems it doesn't have the option to add other headers.