Unable to add multiple expenditure organization for a single BU.

We have 1 BU and 1 Project task owning and 1 Expenditure organization now.We have requirement where the BU is divided into departments and the customer wants to handle the expenditure department wise.We would like to know the possibilty of having multiple Project Expenditure Organization under one BU.
In the setup, Configure Project Accounting Business function has option of assigning only one Expenditure Organization.
Please suggest us if there is any workaround also.