I'm afraid it's not possible to specify a data set as the TYPE=USER matrix in PROC GENMOD.  The important thing about the GEE model that GENMOD fits when you specify the REPEATED statement is that the method is robust to the choice of correlation structure.  So, even if you select a structure that doesn't exactly match the true structure, you still get statistically consistent estimators.  It is usually sufficient to pick a structure that is roughly similar to the structure you have. ... View more