According to the story, Matt really wasn't sure if his bud Sean was making a joke or not (although we've yet to hear Sean Penn make a joke and can't be sure he ever has) and turned it down because he refused to switch to the Democratic Party.
Now, we've done a quick search through the news and couldn't find any damn stories corroborating it and Wonkette doesn't supply any links to the story. So, this could either be Wonkette having a laugh at our expense, and, if so, are you having a laugh? Are they having a laugh? Or, they got tipped onto a juicy-ass rumor that somehow scooped the entire San Francisco media/gossip train. We kinda hope this story is true 'cause besides giving old SFist an actual election to cover, and quite a juicy one at that, the idea of Sean Penn being involved in SF politics and playing money fairy to Matt Gonzalez is just stupendously awesome.