Casting Netflix to a TV while still seeing video on the phone as well?

When I or my girl leave the main TV room to use the restroom or feed the dog, etc, is there a method or a 3rd party app that will allow the casted app (Netflix or HBOGo mostly) to still play on the phone while also casting to the TV? This would avoid having to pause the show we're watching. FWIW, screen mirroring from the Chromecast app while watching Netflix locally on the phone... is way too laggy to be a viable solution.

Thanks for any suggestions.