my $pkg = "Foo";
eval qq{
    package $pkg;
    sub new { bless [], shift }
};
print ref $pkg->new;

__output__

Foo

##</code><code>##

my $pkg = "Foo";
{
    no strict 'refs';
    *{"${pkg}::new"} = sub { bless [], shift };
}
print ref $pkg->new;

__output__

Foo