Discounting order line using a separate line item, link together

Hello all.

Have a request to add a discount to a sales order but to add as a separate line to the SO - not to show as a typical "pricing discount" against the order total or individual lines. Here is the basic ask which I have several questions about the parts:

>The intent of this request is to allow negative values to interface from SalesForce to Oracle as Sales Order Line items. [this will be a customized process to calculate the value - percentage or flat amount across all lines on the quote being importing to OM, and we would allow negative pricing in OM]