If I remember correctly, you can kick the printer into "RAW" mode by;

:Stage 1
SET CONS OFF
SET DEVICE TO PRINT
SET PRINT ON
??? && puts the printer in "raw" mode
??? escape codes to set page length

Stage 2:
Now, remove all the printer-specific data from your report (clear out the EXPR, TAG, and TAG2 fields in the report, or was it label, file).

:Stage 3

print the report or label (with the NOCONSOLE parameter)

:Stage 4
SET DEVICE TO SCREEN
SET PRINT OFF
SET CONS ON

If this doesn't work, check out the EXPR field in the label/report file. It contains a variety of printer settings including page length (it doesn't store the actual length in inches, it stores it as a value. You can play with and see what the value is set to when you set your page length to your desired length). You could then clear out the EXPR (and TAG, TAG2) field(s) and APPEND MEMO to the EXPR field the command line to set the page length. Note, haven't tried this yet but in theory .........

GL
Bill