I agree 100% with sauoq in that you should always try to separate user-configurable stuff from the script itself into a config file of some sort. But again, if you feel that it must be inside your script, in the spirit of TIMTOWTDI, another way would be:

local $/ = undef;
my $user_defined_string = <DATA>;

# script here

# USER:  put your text after the __DATA__ token, but leave that line a
+lone!
__DATA__
blah blah blah
and more of the same
[download]