This is something I have been saying for a long time. The quickest way to legitimize Ultron (or eventually Thanos) is to just have him curb stomp Hulk or shut him down really, really quickly. Maybe do the whole set up of them trying to get Hulk to Ultron, and we finally get the moment of Hulk unleashed on him, and the audience goes nuts thinking this is gonna be awesome.
Then Ultron just pimp slaps Hulk a few times, looks at the rest of the heroes and asks when they are going to pose a real threat to him. That would be a real quick way to establish that you do not fuck with Ultron.
Or maybe Ultron hits Hulk with a beam that makes him revert to Banner, then casually tosses him aside like a rag doll. Then we get to hear Spader go, "Bitch, please. You didn't think I was ready for that shit?"
Sapping the gamma radiation from Banner's body would work, if he had that capability.