Yes, you can - breeders do it - but why? You will always need a larger area when they grow - I have two areas in my pond very deep and a shallow end which they never really go in but I have made the shallow end pretty for me because I can get to it! I will take a pic tomorrow to show you how we have done it. Koi breeders here say 'there is only water' no fish. If your water is right them the fish are very happy.
Actually lost one today because of load shedding, the pump was off too long - not a big one but still. The others were trying to push him/her to the top to breathe it was quite amazing to see, but it still died. I didn't think fish could do that...