New object attribute on start condition

Friends,

I need to configure a start condition for a custom workflow that is triggered by J1B1N (Object BUS2143).

But this WF is triggered even we don't need to work with it, because we need it to start only if the field J_1BNFDOC-DOCTYP = 3 or 5. But this field doesn't exists on the object.

How can I add and populate the field in the triggering event so I would create a start condition with this field ?

Release 46C.