Can't set custom page size in Mac printer driver

I have a Konica Minolta bizhub printer and it has a bypass tray that can accommodate all sorts of custom paper sizes, but I can't seem to make the Mac driver reflect that paper size, so when it gets sent to the printer, the printer interprets it with the default paper size (8.5 x11 in this case). This is coming from an Adobe application (indd and Acrobat both), but no matter what I do in the driver I cannot get it to send the job with the custom page size (16.3x3.7 in this case). All of the posts online for how to accomplish this show a Windows driver.

Question by jamierob on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.