I would second the recommendation that you stop by your local pharmacy and purchase a small bottle of castor oil. 4 oz. to 8 oz. added to a gallon of fuel will provide all the protection you'll want for breaking in your new engine. It shouldn't set you back more than a couple of bucks, either.

I wouldn't just recommend this for break-in, either. I'd recommend that you add 4 to 8 ounces of castor oil to every gallon of 100% synthetic lubrication fuel you buy.