‘Sneakernet’-type reply: Schedule it for each individual 5th (i.e. 090506, 100506, 110506, etc.) for as many repetitions as JOBSCDE will allow. Then setup a separate JOBSCDE to remind QSYSOPR at the appropriate time to revise with new dates before the last one runs.
Crude, but quick. Other, probably far more graceful suggestions, are sure to follow from others.