Bummer... it would definitely be useful to specify a delegate to be executed when a constructor runs. Would be preferable to do it in a strongly-typed manner, though the following might work as well - Isolate.NonPublic.WhenCalled(obj, "MyObject") or Isolate.NonPublic.WhenCalled(obj, ".ctor").
The scenario I'm trying to set up is verifying that method calls occur within a transaction, i.e. set up a list of Actions and make sure that they haven't been called at the time that a TransactionScope object is instantiated and have been called at the time of TransactionScope.Complete().
I was able to get around this, because we have a custom container around TransactionScope, which happens to call a private _initialize method in the constructor and I could set up the DoInstead logic around _initialize. This is of course not ideal, as it exposes implementation.