There are several ways to do this, but none that are provided
Out-of-the-Box.

Probably the best way to do what you want would be to create  a Custom
Field Type. With a custom field type you have complete control over
what and how the column  is displayed. If you add the security trimming
there you could prevent people from seeing it.

I'll give that a try....................

Are you referring to writing code to create  this Custom Field Type or are you
referring to simply adding a UDF column  using the interface? If the latter, how
would you go about security trimming it? Perhaps I'm missing something here, so
I just want to be sure.

Writing code to create  a new Field Type class with supporting XML and
UserControl template to control the display.