Adding an asterisk to parts of reference list

Hi, I'm using Mendeley desktop (word 2011 for mac). I'm writing a report from a meta-analysis, and in the reference list I would like to add an asterisk (*) before the references that were included in the meta-analysis (to separate them from other references that for example were used in the introduction). However, when the reference list is refreshed all the asterisks disappear. Is there any way to achieve what I want to do? Thanks, Daniel