Success!  The key seems to have been in ChromeStar's recommendation to have two separate root nodes and assigning each to a different render engine.  A part of the solution was also taking up Hborre's advice on not plugging Cycles nodes into PoserSurface roots.

So here's what I did.  For each material zone, I plugged my original shader into a CyclesSurface root node and disconnected it from the PoserSurface root node.  I then plugged very basic diffuse and specularity into the PoserSurface root node.  Next, I designated the CyclesSurface node as the root for SuperFly and the PoserSurface node as the root for FireFly.  Finally, I made FireFly the current render engine in my scene, and voila!  While I was at it, I took the opportunity to add a preview shader for the eyebrows, which didn't even exist in my original workflow.

It's not an entirely seamless fix, since it essentially requires switching between render engines whenever I either start or finish rendering an image (e.g. if FireFly is active for preview purposes, I need to switch to SuperFly for actual renders), but it's much less hassle than anything else I thought to try.  For the sake of potential FireFly renderers, I wrote a Python script that will go through the figure's materials and swap the root node assignments.  So FireFliers can use SuperFly in preview and switch to FireFly for rendering.

The best part is that, even if I don't switch to FireFly in preview, the figure displays as light gray.  Although it's still textureless, it at least makes shading visible, which is still an improvement over a dimensionless black blob!  Thanks for the tips, everyone!

And Hborre, I'm glad to hear that the idea of dial-controlled shader settings intrigues you.  Now I know I'm not completely alone.  Maybe it's just me, but it has long seemed like a rather obvious step to take with the advent of animated shader nodes and master/slave parameter relationships.  Frankly, I don't know why fixed presets are still the standard that they are!