If you want to replace Photo-Flo with something you make yourself, and keep things environmentally friendly, perhaps you should consider a green soap solution. This material has been sold in pharmacies for decades (ye gods, I hope you can still get it, it's a critical ingredient in model airplane rubber motor lubricant), and comes in a tincture (alcohol solution) that can probably be added directly if you wash in distilled water (rather than hard tap water).
However, another potential alternative that's much closer to the original product is bubble liquid. You know, like the kids use with that little wand to blow soap bubbles? It's similar strength to Photo-Flo concentrate, non-toxic enough to hand the bottle to a five year old, and costs about fifty cents for a quantity similar to a five dollar bottle of Photo-Flo. And there's no milk or whey in there to make your film go sour...