TAX or another non stock item to GTS

Hello,

We are having a heavy sales order process and users would like to simplify the sample shipping somehow. There are insignificant quantities of them, so we had an idea to make a delivery without order and use an additional item category  TAX or DLX (no stock, bo picking, no TO, no goods movement during PGI) for the materials that already exist and we sell them as TAN.

Then we can create a proforma and a commercial invoice but the thing is that proforma does not transfer to GTS. Is there any reason why we should not transfer TAX/DLX non stock items to GTS ? Can we customize it and what are the cons ?

Thank you very much.

Olaf