Help! Reconsolidate Sales Invoices and Cust. Ledger Entry

We have a request from a client which is unusual and they are intent on getting it in exactly the way described: -

They are producing sales invoices in the usual manner. However, they want to print sales invoices with a different consolidation level, that is by Customer, by VAT Product Posting Group.

So we have 3 Sales invoices: -

Sales Invoice 1, Customer ABC Ltd
=================================
Sales Invoice 1 Line 1, VAT Product Posting Group 1
Sales Invoice 1 Line 2, VAT Product Posting Group 2

Sales Invoice 2, Customer ABC Ltd
=================================
Sales Invoice 2 Line 1, VAT Product Posting Group 1
Sales Invoice 2 Line 2, VAT Product Posting Group 2
Sales Invoice 2 Line 3, VAT Product Posting Group 1

Sales Invoice 3, Customer XYZ Ltd
=================================
Sales Invoice 3 Line 1, VAT Product Posting Group 1


They wish to produce a sales invoice which consolidates by Customer and also by VAT Product Posting Group. So we now have, the lines switch over as shown below (the original sales invoice line description has been maintained). Now, I can see a solution to this which involves maintaining a new no. series and changes to posting routines etc. However, they are now talking in terms of keeping existing consolidation as shown above for the sales invoice document but producing the cust. ledger entry as shown below as well as the reporting changes.

I think this may be very difficult. Can any of the Navision superstars out there give me a bit of guidance as I am out of my depth here. There may be all sorts of consequences with Navigate, Dimensions, Gen. Ledger Entry etc.


Sales Invoice 1, Customer ABC Ltd
=================================
Sales Invoice 1 Line 1, VAT Product Posting Group 1
Sales Invoice 2 Line 1, VAT Product Posting Group 1
Sales Invoice 2 Line 3, VAT Product Posting Group 1

Sales Invoice 2, Customer ABC Ltd
=================================
Sales Invoice 2 Line 2, VAT Product Posting Group 2
Sales Invoice 1 Line 2, VAT Product Posting Group 2

Sales Invoice 3, Customer XYZ Ltd
=================================
Sales Invoice 3 Line 1, VAT Product Posting Group 1

Many thanks Roddy