There's not much formality involved with calling FSS. It's just
"Lansing Radio, N6030E, over."
"N6030E, Lansing Radio, go ahead."
"N6030E would like to open our VFR flight plan from X to X."
"N6030E, flight plan opened. X altimeter XXXX, you have a great flight."
"Thanks sir, 30E."
Even then the briefers aren't subject to a whole lot of phraseology.
If we're talking about giving DF steers, then that's probably not the easiest thing to simulate, but since Lockheed-Martin consolidated almost everyone into Washington, DC, many FSSs don't even provide that anymore to begin with.
In terms of weather briefings, there are many websites that can decode the meteorological information into essentially a script. If anyone's familiar with DUATS (duats.com), the decoded radar reports there are essentially what's read over the radio by both controllers and FSS. I've actually briefed pilots FSS-style on my Denver Center frequency recently when we had a few small but intense cells along a popular route of flight.
I think a HIWAS application would be more valuable than FSS at the moment. At the same time, though, the information presented on it could be really "off" since pilots don't all have standardized weather. Running a HIWAS would be a little bit more complicated than recording something and putting it on the air. First there has to be a way to record it and put it on a VOR frequency. Next you have to allow the pilot clients to receive the VOR frequency, but not the morse code that Flight Sim would automatically broadcast; it would need to broadcast the HIWAS recording. On top of that, a CoC amendment might be necessary in the event that a controller wants to broadcast a Voice HIWAS and Voice ATIS (read: the two connection rule).
I think standardized weather is really necessary before any of this could happen.