Bluetooth SPP in Add-On

I have an Arduino that controls a coffeemaker that I already have integrated to Home Assistant. The arduino has an HC-05 bluetooth module, and I use the serial2mqtt program in a docker container on separate hardware. This all works correctly.

I would like to move the serial2mqtt container to Home Assistant OS in the form of an Add-On. I reviewed the instructions for creating a custom add-on, and it works until I need to open a bluetooth connection via rfcomm. Rfcomm doesn’t seem to be installed/supported/available in Home Assistant OS, and so I can’t use Bluetooth Serial Port Profile to connect to my device. Pairing via bluetoothctl works, but I don’t have the ability to open an rfcomm channel.

Any ideas?