In reply to Paul J Nietert.

See the formula for the NOCENTER option in PROC GLIMMIX. It shows how GLIMMIX standardizes the columns of the design matrix. Therefore, the following are equivalent:
1. For the raw data, use the STDCOEF option on the MODEL statement.
2. Standardize the data by using (x-mean(x))/sqrt(CSS). Estimate the fixed effects without using the STDCOEF option.