WPUUMS - different Company Code for Article vs Bill

Hello,

When processing WPUUMS IDocs from PIPE / POSDM, the Partner Number is the Store Site and the Article and Billing documents generated both have this Site and derive the Company Code from T001K.

Is there a way to have the Billing document post to a different Site/Company Code? I have looked at the user exits (EXIT_SAPLWPUE_xxx) and debugged and so far cannot see a good place to change the Site or Company Code. I'm hoping there is a more standard way.

Thanks!