Allocate overtime based on timecards entered to different projects

Hi,

My company is a project based company paying the employees based on the hours spent in different projects (projects are defined as Business Units).

What we need is when executing the payroll  to automatically allocate the additional pay types like bonus, overtime based on the hours the employees worked to various projects. These hours are entered in the time entry as timecards under pay type 1.

Example:

Employee Std Hrs/Month = 200

He worked lets say in two different projects (BU1 and BU2). So, he entered 2 timecards under pay type 1.One timecard with 120 hrs for BU1 and a second with 80 hrs for BU2.