If you send the message from another sysid then you should send heartbeat messages as well.
There are one semi solution : You can send your messages with sysid=flight controller sysid and with component id = 0 (ALL) this will show up in the drop down
> If you want to display the data alongside with the flight controller you have to send messages with the same sysid and component id as the flight controller.
Sorry I was wrong with this one, the FC will not forward messages it got with it’s own sysid and compid.
Regarding LUA, YURI have an excellent tutorial in this topic.