How to: runs in privileged mode to enable access to the usb devices.
docker run \
  --privileged \
  --device /dev/kvm \
  -e RAM=4 \
  -p 50922:10022 \
  -e "DISPLAY=${DISPLAY:-:0.0}" \
  -e EXTRA="-device virtio-serial-pci -device usb-host,hostbus=1,hostport=2" \
  mycustomimage
```

You should see the device show up when you do `system_profiler SPUSBDataType` in the MacOS shell.

Important Note: this will cause the host system to lose access to the USB device while the VM is running!