If you ggogle "cuttlebug sandwich matrix" there is a file on the provocraft or cricut website with some sandwich instructions:
For brass embossing stencils:
Pad ‘A’,
Pad ‘B’
mouse mat (cut to size, rubber side up),
Cardstock
Brass stencil
Pad ‘B’
Not sure if a mouse mat is the same as a tan embossing mat but I think you need something thicker.
Here is also a youtube video using a different sandwich:
http://youtu.be/LiMpHLOEoPc