I hadn't even heard of the earth day special until recently as well.http://www.youtube.com/watch?v=BAq3fTVTPRU
As you can see, Elon is in a GB flighsuit and appears to be a ghostbuster.
but I'm guessing he would have created "Elon" for trademark reasons. If we consider Elon a canonical character he must not have made much of a name for himself as a Ghostbuster since Ed is known as Egon's nephew rather than Elon's Son.
Just like in the movie Casper, Ray Stantz was not named in the credits but "obviously" thats who he was in the movie.
It's been a while but didn't Egon mention his siblings (not by name) in GBII?
I'm not sure, but I do know that Egon's siblings have been mentioned in the RGB cartoon show before. If not by name.
I think this is a cool little tid-bit and could be the only real missing link to making FvsGB or RotGB officially "canon" in the movie sense.