This (courtesy of google) might give you a starting point.

Perhaps the easiest way would be to 'obtain' a tape (perhaps from whomever you are preparing this for?) formatted to the correct requirements and see if you can read it! Then, if you can, try and emulate it.

From my memory of the late durassic period when I was last involved in playing with IBM standard tape drives, writing a "tape mark" was a single (ioctl?) call to the device. Hopefully your drive has a similar, compatible facility.