Hi Alvaro,
You can make the connection you're describing with the Bpod Teensy Shield, a Teensy 3.2, and a single line mod to the echo module firmware.
The mod is: delete line 47:
Serial1.write(SerialOutputBuffer, outputBufferIndex);
You will then have a module that relays any bytes from the state machine to USB, and any bytes from USB to the state machine.
-Josh