Sales BOM per customer

This might be a strange question but still. We have a customer who ships out pallets and crates to their customers. They want to be able to track these items of course and bill the customers according to the number of items they received. N.B. these items are not returned so returnable packaging is out of the question.

We are looking at the use of a sales BOM so we can calculate the number of pallets and crates per sales order and delivery based on the number of finished products they ship out and of course create an invoice where these items are listed as part of the delivery with the actual costs. This works quite satisfactory BUT it will only work when either all customers use the sales BOM or all customers do not use the sales BOM.

What's the problem, as this is a new process, they will not be able to convince all customers to directly pay for pallets and crates that are being shipped out. We are now facing the problem that for part of the customers they want to use a sales BOM and invoice them for the pallets and crates they receive BUT for part of the customers they do not want to invoice them for the pallets and crates they receive. This means that we are looking for a way where we can indicate, per customer, whether to use a sales BOM (ship out and invoice pallets and crates) or not to use a sales BOM (do not logically ship out and invoice pallets and crates).

Is this possible yes or no? Maybe with a user exit that checks for a specific field in the customer master? We have already defined two sales BOM's per material, one where pallets and crates are used and one without pallets and crates so we could mis-use the alternative sales BOM principle, but we still need a trigger to call either sales BOM.

Any help would be appreciated.