Manual Charges on Sale Order

Dear Guys,

My scenarios is that we add  Bank Guarantee ( Charges) in sale order and AR invoice with item revenue line and take receivable from customers in case of credit sale on Bank Guarantee. For example

Order Line           Item "A"         Amt  : 10,000    ( Assign Revenue account code combination )
B.G Charges                                         2,000     ( Assign Expense account code combination)
                                                        ________
Total Order Amount                             12,000

The accounting entry of above mentioned case must be as follows :

                                                         Dr.          Cr.
Receivable    ( Customer )             12,000
Revenue                                                      10,000
Expense ( Bank Guarantee)                          2,000


I just want to add manual this bank guarantee expense in sale order and assign B.G expense account code combination from COA as per my requirement.How can I do this ?