Split goal management approval flow

Summary:

For my customer we enabled both Line Managers and Functional Managers (matrix manager at employee assignment level) to assign goals in the goal plan of the employees. We enabled the approval flow when the employee tries to assign own goals or modify the existing once. It is the Line Manager that approves. Customer wants that when the employee modifies one of the goals assigned by the functional manager the approval flow needs to go to the Functional Manager..in the other cases to the Line Manager.

Content (required):

The problem I see to achieve this is when the employee performs multiple changes in multiple goals with different source and submits it for approval..I tried and goals doesn't split and go some to the line manager and some to the functional...any ideas?