Headless Sway on Raspberry Pi

Hi all. Hardware is Raspberry Pi 4.
I find booting into Sway will hang without the usb keyboard plugged in. The following log message appears when this happens.
Set WRL_LIBINPUT_NO_DEVICES=1 to suppress this check.
Any idea how to implement this? Where would I look for this code? I wish to start the Pi remotely and then plug the keyboard in at leisure.