I don't see that there is easy CakePHP way. You have to modify /lib/Cake/Model/ConnectionManager.php . In version 2.3 on line 69 there is
include_once APP . 'Config' . DS . 'database.php';
I don't see there any code that allows the configuration. It looks hardcoded.
More elegant way is that you make symbolic links as @Kai mentioned. Then you can upgrade CakePHP without having to remember about your little hack.