Works a treat with some kids.Not sure it will help but there was an episode of Supernanny ages ago where she had the idea to get the child to give their dummies to the 'Dummy fairy', so she can 'send them to kids who need them.' The girl quickly handed over her dummies and hung them from a tree outside so the 'fairy' could collect them, and then they left her a present.
My son used dummies at 4 but he was going through cancer treatment and they really provided comfort for him so we picked our battles. Anything that comforted him during that time was 100% okay for us. He passed away in 2016.
My daughter is 3, and while she never met him we speak about him constantly of course.
We did a twist on the dummy fairy and put her dummies in an envelope to ’heaven’ and gave them to her brother to have. She was happy to give them to him. We told her there wasn’t a dummy shop there so we had to sacrifice ours for him.
My friend did almost the same thing and ‘sent’ them to babies in other countries who were too poor to have dummies. Different stories work for different kids I guess. Worth a try if you’re struggling. It’s hard to get them off them when they’re so attached.