Filled fields with constant text - is it possible?

Hello,

When using filled fields in perl (the ^<<<<< notation), a ~~ at the
beginning of the line will suppress it if the line is otherwise blank.
However, what if I wanted to have a constant text in the lines?  How could
I keep the script from looping forever?  And note: the length of the
filled text is not a constant.

Example:

A user provides a text file that is read in by the script.  I want to
insert it into a rectangle like so:

format WHATEVER =
____________________
~~  | ^<<<<<<<<<<<<<<<<< |
$text
--------------------
.

Ugly, I know, but you get the point.

Any suggestions would be appreciated.

Thanks,

ugly