Force an IDoc status from a conversion exit

Hi,

I have created a conversion exit (FM CONVERSION_EXIT_*_INPUT / tcode BD79) for outbound IDoc FIDCC2. It converts in-values into other out-values by using a z-table. If the in-value is not found in the z-table, the IDoc should not go into status 03 (Data passed to port OK) but remain in error status instead. How/where can this error status be forced?

Regards, Jan