Yes, that should be possible. Are you asking if it is possible, or if someone will code it for you?
The code is not so complex - in the callback that handles MIDI read for the TRS jack, just forward the identical message to the USB midi port.
Catch is: you’ll be merging that data with the 16n’s own data. And bear in mind each fader on a 16n can be on its own channel, so just saying “don’t forward channel X” won’t work. For every message, you’d need to look up if it clashed with 16n, and then ignore it.
Dumb forwarding - just letting it clash wherever - probably isn’t so hard. My recommended way of doing this would be a single #DEFINE to enable it (before doing any refactoring). It’s not so complex a config option to implement. There’s probably also some performance testing to do, to check this doesn’t have too big an impact.