VOFM Requirement coding

Advice sought..

I want to use an Output Control <i>requirement</i> to determine if an event should be triggered by Sales Order Output Control. The value I want to use to decide is the CEPOK flag on the sales order item line. Any line with CEPOK set to 'B' should satisfy the <i>requirement</i>. However I presume the KOMBPV1 structure will only hold a single line.. Which line? and how do I examine all lines? And how come KOMBPV1 doesn't have the VBELN key field? I was going to use some code like:

SELECT SINGLE CEPOK

FROM VBAP INTO VBAP-CEPOK

WHERE VBELN = KOMPBV1-VBELN

AND CEPOK = 'B' OR CEPOK = 'C'.