How would you determine the last FTP logon time/date for a bunch of local user accounts on a DMZ (standalone/workgroup) server running IIS FTP?

I know I could use a log aggregator and sift through it that way, but this server has been operational for approximately 8 years and I don't fancy that vector.

I have also tried the scripting route, but this is of no use because the users have never actually logged onto the machine, so there's no profile (rendering the WMI classes *WIN32_UserAccount* and *WIN32_UserProfile* useless). They're just used to access the FTP service.

Thanks in advance