How to use Protein Design for site saturation analysis

I am trying to using the protein design module to build and analyze the model of single site saturation mutants. I want to mutate one amino acid residue on a protein structure to all other 19 amino acids, and build and analyze the stability of all 19 mutants.  So far, the define mutants dialog only allow me to put only one amino acid type in the mutation column.  However according to the help file I should be able to put multiple amino acid type on to the column. But there is no instruction on how to do so.
Is there is a special script for doing multiple type substitution. 

Thanks for your help

gofish