Based on one of the calculators I found, if your recipe is built to yield a beer that is 1.093, then you should expect to get a second beer of the same volume that is around 1.047. Of course it will vary with your efficiency, but that should be close. So what you'd want to do is get you're preboil volume for the big beer into your first kettle, then continue sparging and draining into your second kettle until you reach the same volume in that one. Again, there will be variables, such as different boil times, etc, but that's the gist. Have fun, and make sure not to lose focus on the big beer for the sake of the small one, it's just a bonus.