my $package_method = 'Foo::Bar::baz';
my $orig = \&($package_method};
no warnings;
*{$package_method} = sub { pre(); $orig->(@_); post() };

##</code><code>##

package Foo::Bar;
sub baz { print "I am the original!\n" }

package main;
sub Foo::Bar::baz { print "I am the new baz!\n" }

Foo::Bar::baz();