use lib 'modules';
use lib 'modules/Client1';

##</code><code>##

package MainApp;

use strict;
use warnings;

use base 'Base::MainApp';

1;

##</code><code>##

use UNIVERSAL::require;

sub runmode {
    my $self = shift;

    $modulename = $ENV{APP_NAMESPACE}. '::FooBar';
    $modulename->require or croak $@;
    $foobar = $modulename->new();

    # carry on... use $foobar as needed
}