[galaxy-user] wrapper question prefix for output files.

Hi, I hope someone can help me on how to implement this into a wrapper. We would like to add an option so the user can set a sample name which then be used for the prefix of the output files names. For example, Is it possible to provide a sample name that can be used to prefix the output files? For example, could I specify a sample name "S" and have the output files be "S.gene_abundances" "S.isoform_abundances", "S.rsem_log", and "S.bam"? I know we can name the files from the xml, but is the a away to allow the user to pass this prefix without having to do a recursive conditional in the xml file to set this prefix? Or any other way people are doing this? Thanks in advance. Victor