Illustrator Drop Shadows are set to multiply by default.
If you are talking about drop shadows from Photoshop placed images, you need to make 2 photoshop files to achieve this.
To get the images to register, you just need to copy 1 oplace image and paste in front, then use the links panel to relink to the other image.
What now? No, just typical Illustrator drop shadows, live effects. But you comment about Multiply Mode . . .
I checked into that. I had turned it off so I could eliminate hard-to-predict print problems resulting from using fancy effects.
Turns out, Multiply Mode makes the shad overprint. The proof:
Overprint on. Drop Shadow blend mode: Normal.
Overprint on. Drop Shadow blend mode: Multiply.
Nice! Thanks, Mike.