How to make alarm sound only over Bluetooth?

I wear hearing aids, with Bluetooth connection to my iPhone. When I stream music or make phone calls the sound goes only to the hearing aids, which is as I want it - one of the few advantages of deafness, in fact! But when I set an alarm it rings on both the phone and the hearing aids simultaneously. How can I make it just ring on the hearing aids? If that isn’t possible with the native clock app, is there a third party alarm app that will do it?