Your premium will take a hit regardless of what the insurer is having to pay out, as will his regardless of fault, so let him think he's getting one over.
It's either genuine and it has infact cracked the bumper, or he's just a tool. Either way, you're best off leaving him to get on with it like a kid in a ball pit, if that's what he wants to do. Depending on if he goes with an authorised repairer, or if he's allowed to source his own garage, it'll come in at £500 easily. If you're down south likely more.