I’m not sure how well it would be received but what if Sinestro just lost the ability to wield any lantern ring, say Kyle Rayner using something akin to his former white lantern powers cuts him off from the emotional spectrum. However as the person he is he can’t accept this and through his shady dealings he manages to create a wide spread empire under his command. To make matters worse to make it so the green lanterns can’t touch him he willfully puts his new empire into the United Planets (yes I know it’s new but it has story potential), giving whatever resources he believes will prove him as useful and making it that should the green lanterns ever come for him they’d be causing an intergalactic war, as well as unintended consequences.