use warnings;
use strict;
use lib '.';

BEGIN {
	sub Foo::ONE () { 444 }
	sub Foo::TWO { 555 }
	sub Foo::THREE () { 666 }
}

use Foo; # _after_ your "re"definitions

Foo::go;
print "One=", Foo::ONE, ", Two=", Foo::TWO, ", Three=", Foo::THREE, "\n";