Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
There's a lot jailbreak tweaks that would get this done. (I assume you're not updating because you're jailbroken.)
Mikoto. It will remove the badge and also physically prevent you from accessing the actual update mechanism. You'd have to uninstall Mikoto on purpose in order to "accidentally" update.
Oh, sorry. I'm not jail broken but want to when the next one is released. I'm hoping to stay at 9.1 just in case that is the version released. Probably not the best place to ask but I had the reminder pop up while checking on jailbreak news...
 
I got an Verizon iPhone 5s from Apple yesterday. The Genius Bar said it was on 8.4 . Tiny umbrella says 9.01. I put it on swappa as it is unactivated with unopened accessories so will make some jail breaker on Verizon ATT or Tmobile a nice Christmas present.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.