Instead of an IO layer, would a tied handle do for you? Here's an example.

use warnings; use strict; use 5.006;

{
package Tie::Handle::CloseAppend;
sub TIEHANDLE {    
    my($class, $string, $handle) = @_;
    my %obj;
    $obj{"handle"} = $handle; # this argument to tie is optional
    $obj{"string"} = $string;
    $obj{"open"} = defined($handle);
    bless \%obj, $class; 
}
sub OPEN { 
    my($obj, $arg, @arg) = @_;
    $$obj{"open"} = 1;
    open $$obj{"handle"}, $arg, @arg;
}
sub _preclose {
    my($obj) = @_;
    printf { $$obj{"handle"} } "%s", $$obj{"string"} or 
        warn "warning: could not print closing string to Tie::Handle::
+CloseAppend handle: $!";
}
sub CLOSE { 
    my($obj) = @_;
    _preclose($obj);
    $$obj{"open"} = 0;
    close $$obj{"handle"};
}
sub DESTROY {
    my($obj) = @_;
    if ($$obj{"open"}) {
        _preclose($obj);
    }
}
[download]

sub WRITE { 
    warn Dumper(["WRITE",@_]); 
    1;
}
sub PRINT { 
    my($obj, @arg) = @_;
    print { $$obj{"handle"} } @arg;
}
sub PRINTF { 
    my($obj, $arg, @arg) = @_;
    printf { $$obj{"handle"} } $arg, @arg;
}
for my $m (qw"READ READLINE GETC EOF SEEK TELL") {
    my $mm = $m;
    my $p = sub {
        die "error: $mm unimplemented for Tie::Handle::CloseAppend han
+dle";
    };
    { no strict "refs"; *$m = $p; }
}
sub BINMODE { 
    my($obj, $arg) = @_;
    binmode $$obj{"handle"}, $arg;
}
sub FILENO { 
    my($obj) = @_;
    fileno($$obj{"handle"});
}
[download]

}

use Symbol;
my $APP = gensym(); 
# Create the lexical handle the old style way, 
# for open can autovivify globs but tie can't.
tie *$APP, Tie::Handle::CloseAppend::, "END";
open $APP, ">-" or die "error opening";
print $APP "Lorem ipsum dolor sit amet ";
# note: perl will close handle when $APP goes out of scope

__END__
[download]

Update: changed line in TIEHANDLE from $obj{"open"} = 0; to $obj{"open"} = defined($handle);.