What is the best practice to get the tracking number from a 3rd party UPS account?

Hi,
We have a customer that has their UPS account that we use for the products we ship to them. However, they also require the tracking number on shipping label that is displayed as well as the tracking number that comes up when the barcode is scanned, should show tracking number from the customer's UPS account. NetSuite said they cannot do this unless we register the customer's account in NetSuite separately (however they do not recommend this method)
But here is the problem with this approach - if we have multiple UPS accounts registered in our account then we will have to tie each of these accounts to a location. If you have an empty location in the registered UPS account then that account cannot be used for all locations. In order to make it usable again, you will have to tie it to a location. If you have only one UPS account registered then no location is needed to be updated on the UPS account.