Shrink a Slice? FreeBSD 7.1

[perikillo]

   Hi people.
   I have been googling without any good info about: How to shrink a slice?

   Case: I installed a new server for mysql, is working, I already install
all the ports I need, them I spend a lot of hours yesterday with this baby,
now this is my current disk layout:

/dev/ad0s1a on / (ufs, local, noatime, soft-updates)
devfs on /dev (devfs, local)
/dev/ad0s1f on /tmp (ufs, local, noatime, soft-updates)
/dev/ad0s1d on /usr (ufs, local, noatime, soft-updates)
/dev/ad0s1e on /var (ufs, local, noatime, soft-updates)
/dev/ad0s1g on /backups (ufs, local, soft-updates)

   What I want to do is to shrink the slice /dev/ad0s1g

Filesystem  1M-blocks   Used  Avail Capacity  Mounted on
/dev/ad0s1a       495    232    223    51%    /
devfs               0      0      0   100%    /dev
/dev/ad0s1f       495      0    456     0%    /tmp
/dev/ad0s1d      5967   4225   1264    77%    /usr
/dev/ad0s1e     15863   1343  13251     9%    /var
/dev/ad0s1g    272313  48823 201704    19%    /backups

  Like u can see, is the last slice I have, is posible to remove that slice
and create a new one?

  I don't have info there yet and is not a freebsd default slice, I know
that I need to umount first.

  I have been reading some post but all I have seen is that ins not possible
or I'm wrong?

  I try to with sysinstall looks like don't let me do this.

  Running FreeBSD 7.1-p2.

  Thanks all for your time!!!