The easiest way is to switch from using SyleCop to using Code Analysis, which is built into VS2010.
If you must use StyleCop, you need to make it work as an activity in the XAML Workflow used during build. The easiest way is to create an activity that launches StyleCop with parameters as parameters. You can then direct these parameters to the process parameters in the assembly definition.
http://msbuildextensionpack.codeplex.com/