Fire sprinklers in grease ducts

Got a project where we are required to now install sprinklers in a long grease duct run. How do yall go about it? This is a retrofit so we can’t get duct outlets welded on by the manufacturer and it’s double insulation inside so we need to extend it about 4inches. Was thinking of using a an extension compression seal adapter for ducts but don’t know if it’s appropriate for fire. Let me know y’all’s thoughts. Appreciate it.