I also think that THEORICALY you could throw in the adjustment the EDM distances between your Control points in the adjustment and constrain them,provided that they are weighted properly and reduced to the ellipsoide.Now it will all depends on the software you use, some may not have the ability to introduce other type of measurements other than vectors.But why would you do this on fixed control points ? Adding conventional measurements between the controls and the unknown points will make more sense to me, you are adding redundancy in your measurements (distances, angles, difference in elevation), assuming again that they are properly weighted and are reduced to the ellipsoide.However. I never had the chance to try it, the adjustment software I'm using won't allow me to do it anyway.