Currently, I think this is difficult unless you have the lua programming skill enough, because it needs to improve the core code of Duplex itself. If you don’t have such skill (I also don’t have it at all), you should wait until it will be done by danoise or somebody others. If you can program lua well, of course you can try it, though I cannot help about such part.
But according to your post, it seems that Tenori-on can be used as a common “one direction” controller already. Then it’s not difficult just to make some Duplex mappings.
( 
Oh, now I have to correct a bit about my former post. Though I had said that there is a 1 octave gap in Renoise, it’s only about the native midi mapping of Renoise. About Duplex, it seems that you don’t need to consider it.)
Then temporary, I tried to make a very simple Duplex map for Tenori-on, just for checking whether it works or not.
About how to treat this file(s), please see this article. I guess it should work, maybe I’m wrong something though… 