Thanks for your reply Atul 
Our requirement is to change the baseline date on the basis of transit time (the time to travel material from Supplier destination to Customer destination) which is over & above normal payment terms. So we cant touch payment term because payment terms are assigned to many customers and the distances are not the same for each case & customer.
I am looking for only standard SAP Solution where transit time can be defined at Customer Level. Creating Z scenario with an exit is the simplest way to address this issue but we don't want to do this.
I think the requirement is now more clear to you.
Please help,
Thanks,
Debasish