The creamy head is the product of nitrogen in the beer instead of CO2. You can force nitrogenate in a keg. It's not proper beer though plus it'll knock any aroma dead.
Like the guys are saying, you need to get a N2/CO2 mix to 'carbonate' your beer with, plus a stout tap with a creamer nozzle. If you've already got a cornelius keg set up then it shouldn't be too big of a deal.