It's probably better to require them put their message in another file and then read that in with your script... but, if you are set on allowing them to edit the script, I suggest using a here document with single quotes:

my $message =<<'END_OF_MESSAGE';

They can put pretty much whatever they want in here except for the 
string 'END_OF_MESSAGE' on a line by itself.

END_OF_MESSAGE
[download]

-sauoq
"My two cents aren't worth a dime.";