Please do not date this girl, it is unfair to her, unfair to your boyfriend and basically unfair to yourself to go through such a situation to please your dad.
Unfortunately your stuck in a situation where this sort of thing can not and will not go away with your dad, and you can't come out to your dad, so you will be stuck in this never ending circle, because if somehow you got him off your back over this one, soon it will be another and another and another.
I am so sorry you are stuck in this situation since I cannot suggest any idea to help you since your min problem is your dad not the girl, the only thing I think you can do then is let him have a fit over you refusing to date this girl, it is better for him to throw a fit over that than to Have to come out to him right?
Best of luck, I am sorry you are stuck with such a father, my father too is homophobic and racist, whilst myself I am straight, my cousin on my dads side just recently in the past year admitted to my mum he is gay or bisexual he is unsure and left his wife, my mum has decided to not tell my dad since she doesn't want the family to split, since we are close to my dads sisters family. Also my cousins own father has since left , headed for divorce which I suspect due to finding out about my cousin and yet my father doesn't know the reason yet my dads sister just tells him things didn't work out between her and her husband anymore.