This seems to be a popular request. There's a
suggestion on Connect that deals with this, and it has a good number of votes. That said, I don't see it happening for version 1, because that feature set is (or should be) pretty well locked down. If it's possible at all, you'll have to go in and manually configure the required services on the WHS machine; there won't be an interface.
More likely it won't happen at all, because WHS isn't designed to live on the edge of your home network. That's where your firewall belongs. Still, if enough people want it, Microsoft may decide to include it, so you should weigh in on the feedback I linked above.