Look at this shit I dug up. Randy Stair almost definitely posted on /co/.
It started with an anon posting this video in another thread. https://www.youtube.com/watch?v=JT-bGWcTzw8
The video is about Randy being the first person to upload an HD copy of Ember's song Remember to YouTube.
I remembered seeing this exact video in a /co/ thread before, so I wanted to look it up and listen to it again. What was weird was how the Anon who posted the link was talking about Ember. He really seemed to like her more than most and even knew her backstory that was never mentioned in the cartoon.
So after I had the the exact link to the YouTube video, I wanted to see when else it was posted to /co/. The very first time it was posted here was almost exactly a month after it was uploaded and the OP was talking about how Ember was his waifu forever. Then there's this other thread where the OP says something about Elliot Rodger coming back as a punk rock ghost, just like Randy wanted to happen.
While there's no guarantee these are Randy or even the same anon, I think it's pretty spooky to see shit like this. Hopefully I wasn't too autistic when I put this together and someone else gets a kick out of it.