Ok, now that Poser implements a dedicated "Displacement node" for Cycles, it's now possible to have a second skin with visible thickness

Ooh, that's so neat! I'll have to try this.

Once you guys have a method, would you please explain it to us mortals as well? Thank you!

This is a quick setup using an architectural prop created for Firefly.  I added the CyclesSurface and PrincipledBsdf nodes for Superfly rendering.  Notice, the latest version of Poser 13 now includes a Displacement node.  Plug the Displacement map into the Height channel and adjust the scale.  

The images below show Superfly renders without and with displacement.

The only modification I introduced into the shader was creating the Displacement map with increased contrast to darken the crevices and creases. Subdividing the mesh will improve the displacement quality, especially with organic figures or props.  

Lol... HBorre's example made me thin to... Snarly's Snow Machine.
As it's still an old Python 2.7 script (yet...), I've launch that good old Poser 11 (remember? it's a portable program...), dropped some snow on a rock.
Then, I had to find the three essential nodes: SSMTheSnow, SSMBump and SSMDisplacement. The were only moved, no parameters changed, as it's just an experiment.

With an HDRi, it gives this:

Note the new Displacement node's scale: forced to 3 to have some snow on the almost vertical parts.

What do you think?
If there's some interest, I could port the script to Python 3.7

Sure.  That looks great!

Definitely interested if you could port the snow script, sir!