Using mapsize in variable substitution

[Ian]

How do you dynamically place text (eg. a copyright notice) in the bottom
left corner of the map using the mapsize attributes? For the copyright I am
using:

LAYER
  #
  # COPYRIGHT
  #
  NAME copyright
  STATUS DEFAULT
  TRANSFORM FALSE
  TYPE ANNOTATION
  FEATURE
    POINTS
      10 600
    END
    TEXT '© 2006 Me'
  END
  CLASS
    LABEL
      TYPE TRUETYPE
      FONT tahoma_bold
      SIZE 8
      ANTIALIAS TRUE
      COLOR 255 255 255
      FORCE TRUE
    END
  END
END # LAYER

So in the FEATURE POINTS section I need something like 10 %mapsize.height%-5
but haven't found any examples of people doing this. Thank you.