Jared,
Because the SA series uses a software algorithm for image rejection, it is not a good candidate for EMC precompliance (except possibly for measuring fixed clock harmonics).
We will be adding a preselector to the BB60D, which should be out later this year.
In the short run, assuming you are focused on accurate harmonic measurements, a high pass filter to remove the fundamental but pass the harmonics is a good solution. Mini Circuits has a collection of low cost SMA high pass filters.