As the accessory port is being ignored as an output port here (I haven't found here it's used somewhere), I created script that sends text string to the port.
Spoiler :
acsend.sh:
Code:
#!/bin/sh
Connect the LED to the port and try it with ./acsend.sh 'Hello World!'!
Timing is very unreliable because it's shell script, but it's not bad anyway.