Hi, thanks for posting!
The best way to handle this situation would be to find the property or build step inside your .proj that involves executing FxCop, and marking it with a condition so that it will only execute if NCrunch isn't present.
You'll find an example of how to implement this
conditional build behaviour in the documentation.
if you're running Code Contracts, also make sure you have the NCrunch configuration setting
Allow Static Code Contract Checking disabled, as this can also significantly increase your build times.
I hope this helps.
Cheers,
Remco