To post Packing Slip for multiple Sales Order

Hi, I have written following code to post  Packing slip for multiple Sales Order, I am able to select Customer Account and also able to post all the Packing Slips belongs to selected Customer Account. 

But it generates different Packing Slip for every Sales Order belongs to the same Customer.

I want to post multiple Sales Orders to one Packing Slip.

//code 

SalesFormLetter salesFormLetter;

SalesTable salesTable;

;

salesFormLetter = SalesFormLetter::construct(DocumentStatus::PackingSlip); salesFormLetter.showQueryForm(true);

salesFormletter.update(salesTable,

                                            systemDateGet(),

                                            SalesUpdate::PickingList,

                                           AccountOrder::Account,

                                            false,

                                            false);

//End 

 Can anyone help me on this ?

Thanks & regards,

PAB