You can use hook_theme_registry_alter()
Here is an example of its use in a custom module that works for me (Just replace 'mymodule' with the name of your module):
/**
* Implementation of hook_theme_registry_alter()
*/
function mymodule_theme_registry_alter(&$theme_registry) {
$template = 'node';
$originalpath = array_shift($theme_registry[$template]['theme paths']);
$modulepath = drupal_get_path('module', 'mymodule');
// Stick the original path with the module path back on top
array_unshift($theme_registry[$template]['theme paths'], $originalpath, $modulepath);
}
Now, Drupal will check your module folder for node template overrides.