Thank you all so much. I'm delighted that I don't need to go to the store for one thing!!!!

I'd use up to half a cup of whole wheat flour. Much more and it might get denser than you'd like. You could also use some cornstarch, but I agree with hardlikearmour that using the cake flour in combination is the way to go.
I make an orange cake with ground nuts instead of flour, so that will work, but change the texture a lot.

I say use the cake flour in this recipe rather than the whole wheat.

I'd go with a blend, personally. 1/4 cup wheat and 3/4 cup cake. I think the nuttiness of the wheat flour would complement the orange and olive oil, but a whole cup would be overpowering. Cake flour has less protein, so less gluten development than AP flour.

It's an orange/olive oil cake, one layer. Calls for 2-1/2 cups flour. I have about 1-1/2. I also have cake flour. Would that be a better choice?

If it's whole wheat cake or pastry flour, go ahead & experiment. Just be aware it will change things, but who knows? You might like the result better than your original recipe. If it's whole wheat bread flour, definitely don't use it.

Oops, I said loaf but I meant layer.

What kind of cake? Were you considering using one cup whole wheat with the regular flour? Most recipes wouldn't benefit from using whole wheat but it depends on the recipe. Maida Heatter has a whole wheat pound cake flavored with ginger and coffee but it's rather dense, more of a coffee cake.

By any chance, do you have nuts you could grind up to use instead? Ground almonds, walnuts, or pecans held aloft by whipped egg whites can make for a great cake.

Alternatively, perhaps you could reduce the recipe to make cupcakes or make one loaf and fancy it up with fruit or whipped cream toppings.