Create a class in the normal way and use overload to overload the reference to produce the value in a string context:

c:\test>p1
package Enhanced::String;

use overload '""' => \&asString;

sub new {
    my $class = shift;
    return bless { string => shift }, $class;
}

sub substr{ 
    return substr( $_[0]{ string }, $_[1], $_[2] ) 
};;

sub asString { 
    return $_[ 0 ]{ string } 
};

package main;

my $obj = Enhanced::String->new( 'the string' );;

print $obj->asString;;
the string

print $obj;;
the string

print $obj->substr( 4, 3 );;
str
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