Hello,
The problem with the standard addon board is its size, it can't fit Boxy Pixel shell :S
To connect a joystick, you need at least 2 analog inputs, this is done on the addon board using MCP3021A ADC chips.
The current GPIO driver is also able to use ADS1015 ADC chip, so I think the easier solution could be to use this (or its Chinese counterpart): https://www.adafruit.com/product/1083
Note: The Chinese version is smaller but make sure to not take ADS1115 version, theses are too slow.
The problem with the standard addon board is its size, it can't fit Boxy Pixel shell :S
To connect a joystick, you need at least 2 analog inputs, this is done on the addon board using MCP3021A ADC chips.
The current GPIO driver is also able to use ADS1015 ADC chip, so I think the easier solution could be to use this (or its Chinese counterpart): https://www.adafruit.com/product/1083
Note: The Chinese version is smaller but make sure to not take ADS1115 version, theses are too slow.