I agree with Sandra....this test should be done under the supervision of a pediatric endocrinologist. 

Sandy, your pediatrician isn’t making "excuses".....he is being responsible by admitting that he does not have the expertise needed to properly diagnose your son.  Sorry, but I think it would be extremely foolish for him to perform a test he feels uncomfortable about performing, then interpret the results based on information supplied by the patient, which may or may not be accurate.  For your son’s sake, I hope he is a better doctor than that. 

While I sympathize with the practical concerns that you face, there is no point to doing the test, if it is not going to be done correctly.  The actual test may be able to be done at the ped’s or at a local lab....but it should be done under the direction of a qualified peds endo.  And, the results should certainly be evaluated by a qualified peds. endo.