how to write OM extension to copy Buy line warehouse details to Return line within the same order

Hi Experts, Need your advice like, how to achieve to copy the warehouse details from Buy line to Return Line within the same order. requirement is sales order created with two lines one is "Buy" and another is "Return with Receipt " line, when customer dont want to buy the product then then going to return it, so when customer confirmed CSR team is entering it manually currently but now they want it automatically. can you please guide me how to achieve it this through OM extension or any other easy process to achieve this ?