[Users] Rating Engine ?

Dear List, As some of you know, there would be an open-source-billing for OpenSER, i can see call duration,add remove edit users etc features but missing thing is rating. Since there may be more then one rating table it's very hard for MySql to query whole database and gives time out errors. I can manage PHP to create/delete/edit a new database with prefix,location name,initial time,initial cost,increment time,increment cost and rate id. Now there's a problem, think that there're 2 different rate table for different customers, a rate id is what i would like to write to acc table in each call. May be i should force ACC module to add rate_id together with other information like from_uri, to_sip, timestamp etc. etc. How can i manage this, is there any clue or information ? Thanks, Ozan Blotter