Force cellular data use while connected to wifi iPhone 6 and apple tv 4th gen

I have an unlimited data plan for my iPhone 6 and have purchased the Apple TV 4th generation. I want to use my cellular data connection for obtaining my streaming videos and I want to use my wifi to mirror it through the Apple TV to my big screen. I have wifi assist turned on and am connected to local wifi. My local wifi is connected to my printer and apple tv but not internet. Currently, it senses the wifi connection but will not use the cellular data while connected to wifi. I can't make the phone a personal hotspot because that would require switching to a limited data plan. How can I make the phone use cellular data for internet service and route it through my wifi to the tv?