Adding logged in user name to clicked URL's


I currently add logged in user names to any mp3 links clicked on my web site. I then scour the server access log files for the name variable and add log file data to a database. I can then guage the users file download activity and take appropriate action ie send emails etc. Can something similar be done using piwik and maybe 7tag? Would I use the api to get hold of the users download info? If so, is 7tag available on the free piwik edition?