Customer Shipper Account Number Capture as a option

[cristase]

I'm hoping the community can help with a challenge have on multiple stores.  We sell to some larger customers who some times want to provide us their shipper account number so that we can bill them.  We don't need to provide actual costs or anything.. just a way to capture the shipper and account number.  Ideally this is in the shipping phase of the purchase.  Does anyone have a way of doing this?