whoops! I missed that version number... 1.48.93? Any reason you're not using at least 1.49.01? It was a free upgrade. You might end up saving enough time using the wrapper material in to justify the upgrade cost to 2.0. Depends on the learning curve required to do this all in post, and time it takes to actually get the result you want.
Andy- I don't think there's really any other way around it, excluding what has already been discussed, aside from doing two separate render passes. One with just the model, and the other with the ground plane. That's how I would have done it back in the day.