I just ordered one of the car adapters from PC Torque about 2 hours ago.
I'm pretty sure that you'd find that nothing but a genuine Sager car adapter will work due to the nature of the connector (I've never seen that on any other laptop), and due to the current demands. Most laptops use *far* less power than a Sager, so their car adapters are rated for far lower current/watts.
The only other hope would be to get a power inverter to power your AC power supply, but you'll need to make sure that it can safely handle (I think) 240 watts since that's what the AC power supply draws. Conversely, the car adapter draws (I think!) about 120-130 watts since it's not having to lose some efficiency through a lot of power conversion.