To include this feature in the current software was not trivial. The main idea was to define a new macro (WANT_TWO_FACE) and play with it around existing calls to HT1632 functions. This was the idea. The actual implementation is quite messy and spreads over 18 or so (mostly the "app") files. In any case, I only beta-tested it with 2 displays and works in all modes except "Big" (I didn't bother to investigate yet).
Here are a few photos.
Next round of testing should cover the 4-display 2-faced clock, that is, 2 displays on each side, like a double dual Wise Clock (I know, it's confusing. I will probably ask permission to rename it "Single Kandinsky Wise Clock" and "Double Kandinsky Wise Clock" since I am running out of attributes. Just kidding.)
On a different front, my friend Nick built a 4-display Wise Clock 4 and sent me this photo (plus a set of laser-cut plates to build one myself too; thanks again Nick). Apparently, the software for the 4-display clock has some bugs, so expect soon a new code release (which will include the "two-faced" feature as well).
And lastly, I found this board on ebay. No, I did not buy it (and I am not going to). Just look carefully at the photo and think how you would actually use it, with a knob inserted on the pot's shaft.