Auto accounting rules for planned purchase orders ?

Hello,

Currently in our instance the charge account is not getting defaulted for planned purchase orders.

What is the best way to auto generate charge account for planned purchase orders ?

The criteria could be/may be,

a) expense account from employee record of the buyer/requestor

b) cost center or/and nominal code from expense account rules based on the chosen purchasing category

With the option for buyer/requestor to override the segments.

regards,

kate