Well, it seems you're only dividing for practical purposes at the mixing stage as you have to bake four sandwich cakes. Did you put in half of everything else as the recipe states? If not your 700g won't matter obviously. If you have just prepare the whole quantity of all ingredients and make a fuck-off batch of mixture for all four cakes, then cling film it while you're baking the first two sandwich tins. You might lose some air and therefore lightness of the second batch, but it won't be as bad as using twice as much flour.
I HATE recipes that do this; divide the quantity in the method as I've always suffered from not being brilliant at the recipe equivalent of reading the question.
Thanks everyone. Yes, I did 1/2 of everything on my second batch but put the full amount of flour in instead of 1/2. So, I baked it to see what it would turn out like and it was enormous, dry, and pale. But it did taste nice! I did another one as too ashamed of it to present it to anyone!