Quoting "Darrin B. Jewell" <dbj@netbsd.org>:

> It would be nice to have platform independant disklabel support, or
> at least cross platform disklabel support that could easily be
> reconfigured at compile time, but no one has stepped up to that
> plate yet.

I have a device driver which allows to map arbitrary ranges of sectors from 
multiple devices into a disk device.  Using this driver it is possible to do 
disklabel reading/parsing in userland, which makes platform independent 
disklabel support a lot easier and more flexible.  If that solution (or 
something along that line) suits everybody's needs, I would offer to do the 
work.

Charlie, if you want a more permanent solution than the in-core disklabel:  
You can use ccd to combine your disk and some unused partition on another 
disk (or (a partition in) a small vnd device) and then define partitions in 
the ccd's disklabel which correspond to the partition(s) on your OS X disk.  
The ccd disklabel will be written to the first component, you have to put 
your OS X disk 2nd.  Something like:
  dd if=/dev/zero bs=1k count=20 of=tmpdisk
  vnconfig vnd0 /tmp/tmpdisk 512/10/2/2
  disklabel -I -i vnd0
  define partition a:
   a:        20        20        ccd         # (Cyl.    1 - 1)
  ccdconfig ccd0 0 0 /dev/vnd0a /dev/wd2d
  disklabel -I -i ccd0
  define partitions with offset 20s (=size of vnd0a)

-- 
Christian Limpach <chris@pin.lu>