Autocomplete on Requestor Field

Good Afternoon Everyone,
We were looking to see if there is a way to add to what fields are searched when autocompleting Requestor field. Right now it appears to be searching and autocompleting on the name and email address fields but we would like to add an username field we have. We looked on the System Configuration page and inside the RT_Config and RT_SiteConfig files for some information we found about version 4.x.x but it doesn’t appear to us to be the same for version 5. If anyone has some information that can share, we would appreciate it.