This is a drink which can be nice with all fresh and natural ingredients. Make your own grenadine (using freshly processed pomegranate juice which is magenta in colour, please don't get the bottled ones which are dark red in colour), fresh lemon juice and a cheat's homemade ginger ale (which is fresh ginger juice syrup and soda). The fruitiness of pomegranate plays wonderfully with spicy ginger.
Chris, I used an honest-to-goodness homemade grenadine - a recipe I love and have made for years - and the taste of it in the ginger ale (Fever Tree Refreshingly Light) threw me off. But I agree that it might be best to go all homemade with this. I'll try your ginger ale suggestion.