I recommend you use the "Unlimited health", "Unlimited ammunition" , and "Unlimited Focus" codes for this. Use Focus and try to disarm the Agent. It may take a while, but eventually you should get it. Once the Agent is broken, you can punch and kick him and he will not react. He will simply stand there and straighten his tie every once in a while. If you try to shoot him, he still dodges the bullets as normal.