TypeMock performances for large projects

We're investigating a performance issue in our unit tests.

The issue is that NUnit [Repeat] attribute makes unit tests run 100 times slower than using a for loop inside the test. The time is visibly not from the SetUp and there is a clear overhead running any test case. ANTS profiler seem to indicate that all the time is taken by the assembly loading a reflection calls to check attributes. Sadly it's not visible if TypeMock if doing those calls to for its [Isolate] attributes or if it's something else.

I was wondering if you had some suggestion or insight on such issues.