Have you thought of writing a small assembler program? You can specify the LRECL in your BPXWDYN call, and the DCB does not need to specify an LRECL; it will get it from the DCB parameters at OPEN time. A program to simulate IEBGENER is quite trivial.
Alternatively, look at calling SORT with a FIELDS=COPY parameter. SORT doesn't need the LRECL either. Or write a REXX script.
There are many ways of doing this; you just need to look outside the COBOL box.