How to expand NeoTrellisM4 with tiled NeoTrellis boards?

[okyeron]

The NeoTrellisM4 library for Arduino seems to be lacking functionality to tile additional NeoTrellis boards to expand the button grid.

This seems very odd as the NeoTrellisM4 hardware was obviously designed to be tiled with additional NeoTrellis boards.

Looking at the original NeoTrellis library, it appears to be incompatible with the M4 library (trying to use Adafruit_MultiTrellis with Adafruit_NeoTrellisM4 objects throws errors) - what can be done to get the M4 library to inherit whatever parts are needed from the original NeoTrellis library?