Take a VB file, prepend a static value at the front, write out the record as FB and with a far larger LRECL. My test file is LRECL of 300 (data 296 + 4 RDW) and the longest record is 214 bytes - 218 with RDW. My target LRECL is 500. The value to prepend is 'TAX;' (sans quotes so 4 bytes). I reckon I should have control cards doing something along the lines of:
Errr, hmmmm.... just tried that combination and it worked! But I will post anyway as it may help someone else (or me when I need to do something similar down the track).