How to bill expenses to different customer using Contract billing

I’m trying to find a way to include a company billing in JDE. I explain how they do (I hope It’s understandable). Let me know if you find any way to bill using contract billing (or any other module of JD Edwards):

-          They post expenses in different accounts which should be rebilled to customers.

-          At the end of each month they bill cumulative amount minus previous month billed amount for each account to their customers. They bill to each customer a predefined percentage of each line.

I thought about T (time and labor) lines in contract billing using mark up % and cross account references. The problem is that each expense transaction can only be billed once and we would need to bill once for each customer (each one with different %).