Well, you may get the client IP address from the last user logon (as it is described below in the tread) and then use GeoIpHelper to resolve it.
Essentially you can query cms_user table
select Convert(xml,UserLastLogonInfo) from CMS_User Where UserID = 53 UserLastlogonInfo
will contain xml like so:
You can grab the ip and resolve it with GeoIpHelper