Funds Mangement - Multiple Account Assignments in Stock procurement (PR/PO)

In any unassigned Purchase requisition / Order ( purely stock procurement, not for an order, cost center etc.) it is understood that Fund center has to be entered manually if it were to consume budget. How can i assign multiple Fund centers for a single item of a PR/PO.

e.g. I am procuring 100 units of a material, of which 50 item should consume budget of Fund center1 and other 50 should consume budget of FC2.

In ME51N screen, multiple account assignment icon is disabled unless we give account assignment category other than blank. is there any enhancement / exit that can be used to make it available to assign multiple fund centers.

Thanks in advance

Chris