I like maris' plan. Since the ex-wife of Bobby won't expose him, for whatever reason, the best strategy would be for Ishmeet to secretly marry Pankaj, and him to be around, and the next time Bobby tries hitting on her, Pankaj can intervene and attack him for hitting on his wife.
But I think the other way it can be done is Preeto herself accusing Bobby of hitting on her, making it a he-said, she-said. Ishmeet told her not to tell about her, but nothing can stop Preeto from saying that about herself, and Bobby did hit on her, thinking she was Ishu. So she can design it so that Bobby slips and lets out that he was hitting on Ishu, not her, and thereby be exposed. If Pankaj actually wants Meeta, which is the idea I got from his conversation, then the above plan is no good. But even then, I wouldn't want Bobby for Ishu. Get another guy