1. Do your shadow as a drop shadow rather than one with AE's lights.
2. Make your background white, precompose, and use the free unmult plugin on the precomp (although, now that I think about it, that would do some screwy things with the rest of the footage...you would need to make another copy of the precomp comp without any background (or shadow) and use that on top of the Unmulted one to keep everything opaque.
3. Create a shadow by copying the layer, filling it with black, rotating it, masking it, blurring it, and lowering the opacity.
- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')
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