Automatic GL determination in PO w.r.t. cost centre

Hi,

The requirement is as below.

For a account assigned PO GL should be determine automatically.

For example: Suppose user is creating a PO for a Cost Center .So when user mention 'K' as account assignment category then system is asking to enter cost center.Now when user enter cost center let say 1000 then GL should determined automatically based upon that cost center.

I have tried it with OBYC setting (GBB-VBR) and also checked OKB9 but every time GL is picked prior to enter Cost Center.

Business is planning to maintain GL with respect to cost center . For example

Cost Center A--------------GL 100000

Cost Center B--------------GL 200000

Cost Center C--------------GL 300000

etc.

So depending upon cost centre GL account should pick in the Purchase Order.

Please give your valuable inputs regarding this.

Thanks in advance.