Controlling movements with Nyboard/OpenCat code from a Pi0

First, the Setup:

The hardware switch is set to Ny, not Pi; for reasons already shared from others. So Bittle is awake, but not receiving commands from the Pi0. (If switched to Pi, as others have found, the sketch doesn't correctly load and Bittle is dead.)

What we're trying to do:

We want to be able to control Bittle from the Pi0, without having to write an entire program on the Pi0.

The Pi0 is setup as a Wireless Access Point and we are communicating with it directly from a smartphone with its own network name and a dedicated IP address. That all works fine.

Problem/Question:

Is there a way to have the Pi0 access and control the movement commands on the OpenCat via a serial connection from the Pi to the Nyboard, when the Pi is mounted on the 2x5 pin connector?

If we hook up the Updater module, (without the Pi0 mounted), to Bittle, we can send commands, (like ksit, etc.), via the Updater and Bittle responds just fine.

We should be able to do the same from the Pi0, but can't.

Any ideas of how to get this all talking together without writing or moving the entire sketch to the Pi?

It's really close and acts like it wants to do what we want. But I think we're missing something hopefully very simple and easy.

Please advise - thanks! :-)