Hi,
Thanks for posting.
I admit that I'm not sure how bower and gulp are integrated into your build, but normally build integration is done with custom build targets hooked in with build <Import> tags inside the project XML.
NCrunch has an environment variable that it always sets when building your project. It's possible to use this to create conditional build behaviour. See
http://www.ncrunch.net/documentation/troubleshooting_ncrunch-specific-overrides for more information on this.
If you can find the gulp/bower build targets or imports, you should easily be able to use this to suppress them for NCrunch builds by adding an MSBuild condition to the Import or target invocation.