LARAVEL

<?php
$config['database'] = [
    'main' => [
        'driver'    => 'sqlite',
        'database'  => __DIR__ . '/../database/main.sqlite',
    ],
];

// 個別DB設定を全部require
$req_dir = [__DIR__ . '/database/'];
foreach ($req_dir as $r) {
    foreach(glob($r.'*') as $file){
        if(is_file($file)){
            require_once $file;
        }
    }
}

<?php

use SomeModel;

class SomeController extends BaseController {
    public function someMethod()
    {
        $someModel = new SomeModel;
        $someModel->setConnection('DB2');
        $something = $someModel->find(1);
        return $something;
    }
}