Out of space making backup

When making a backup of my database I run out of space.  I tell it to
put the backup file on my K: drive, which has tons of free space, but
during the backup postgresql creates a temporary folder on my C: Drive
where it initially writes data.  I don't have enough space on my C:
drive for all the data and so I get an out of space error.  Is there a
way to have postgre use one my drives with lots of free space for the
temporary folder?  I'm using version 8.3.9-1.

Thanks.