accounting method

Hi, I just installed new Freeradius server (2.0.5) using LDAP and mysql for accounting and it's all working grate. I want to change the accounting method so instead of adding one accounting record with NULL at the acctstoptime field at accounting start I want it to be one record for accounting start with the code 1 and another record for stop with code 2. That way I can monitor user concurrency and so . I tried to google it and didn't found anything useful for this , is there anywhere I can read about this or anyone can help me here regarding this? Thanks in advance , Ram