Hi,
You can automate the GI with the backflush, which will be exucted during the confirmation of your order.
If you still want to do it at the time you execute COWBHUWE, try to work with User Exit MBCF0002.
One option could be to execute the GI using BAPI: BAPI_GOODSMVT_CREATE. This should be done in the Exit MBCF0002.
Kind Regards,
Mariano