Here's my idea I'm afraid I did not quite have time to get it completed as I've had lots of other things on.
My first thought was what is the cheapest MCU I can find? I spotted the ATTiny10 chips for just 25p each so bought a handful of these along with some surface mount LEDs and resistors.
These would be powered from some button batteries I just happened to have lots of.
The nodes would be spaced out on a clear plastic sheet so you could see that there was no physical connection between them.
They would provide a synchronised pattern or message.
So how does the synchronisation work you ask? Well that would be done by using a camera flash and the LEDs acting as a sensor (a trick I learnt from the Microbit).
Unfortunately I only got as far as wiring up the ATTiny to some wires and the LED to some wires. I do have a programmer for the ATTiny but I've not tried programming it yet.