Create Return Programmatically

Commerce 11.

I have used this as a reference point: https://world.episerver.com/documentation/developer-guides/commerce/orders/using-the-return-order-form/

And while I can create and process a return in code I am missing a few bits of information that I can't seem to set in code.

Specifically the Totals information and the Total Before Return value on the line items (see image) I can't see any documentation which indicate how these are done.

Any documentation or help would be great.

Image:

http://i64.tinypic.com/11wc7ie.jpg