Networking: Client Side Prediction with Inertia

I've been stuck on network code for a while. I'm trying to do a multiplayer top down space flight sim similar to Space War / Star Control. Without rolling my own physics solution, I've found it impossible to do Client Side Prediction as I can't fast foward or manually step a simulation using the built-in physics. I tried Farseer physics, and I can't figure out how to clone & step with that engine either.

I'm trying to implement what is discussed at the bottom of this link http://keithgould.com/post/28875536272/realtime-inertial-multiplayer-games-in-html5 :

Solution in the face of Inertia:

We have a local ship that is moving right away due to our use of client-side prediction, and we have a snapshot that is somewhere in the past. We need to ensure we obey the server. So what do we do? We measure the lag (round trip time) between when we issued the pilot control and the snapshot from the server that acknowledged the pilot control, and we locally fast-forward the snapshot by that amount of time, as well as all future snapshots, and we render off them.