use Module::Build;

my $build = Module::Build->new(
     module_name => 'Foo::Bar',
     license => 'perl',
    );

my $install_dir = $build->prompt(
  "Where should I install to?", '/usr/local/install_here');

# This is what I am looking for. ##################
                                                  #
$build->set( install_base => $install_dir );      #
                                                  #
###################################################

$build->create_build_script;