An Uber Stealthcast is a Stealthcast that is launched with absolutely no promotional efforts.
Whereas a Stealthcast will typically have one type of notice, typically a singular post via Twitter, an Uber Stealthcast will have no notice.
Specifically, it is a very low-key webcast, typically catering to a small audience that may be in the IRC chat room associated with a video feed.
The phrase was started by YouTube and uStream content creator, Alfred, who wanted to reciprocate entertaining video content, via a webcast, for those who were tirelessly monitoring his IRC chat room.
"Holy cow, I didn't even know he was doing a Stealthcast, I didn't see a post on Twitter!"
"That's correct, he didn't post one. It's an Uber Stealthcast"