can't use correctly 'Payment terms' for POs that Lines amounts do not match payment terms

Dears,

Our client case is as follow :

They Buy  an Asset with 2 services :

1. Asset : Server ( 12,000 $)

2. Service 1 : Installation (5,000 $)

3. Service 2 : Training  ( 3,000 $)

Total = 20,000 $

The payment terms are :

1. 50% of the total When they receive the Asset  ( 10,000 $)

2. 40% of the total when it is installed  ( 8,000 $)

3. 10% of the total when the training is done ( 2,000 $)

How can we enter this case in Oracle using ( Payment terms available in PO Header) as the amount of the items are not matching the amounts to be paid each time

Modules used are :

- Purchasing  ( to create the PO via BWC)

- Service Procurement ( To receive Services  by Work Confirmation)

- Inventory ( to receive the Asset)