Anyway, I found an example of the correct syntax in ManageFeaturesController.php. I was flying a bit blind before because there wasn't anything relevant around the hook.
array('select', 'jquery_source', array('auto' => $txt['jquery_auto'], 'local' => $txt['jquery_local'], 'cdn' => $txt['jquery_cdn'])),
I thus adjusted the code as follows, because I noticed the version I cooked up based on Admin.template.php didn't save:
function UAD_integrate_general_mod_settings(&$config_vars)
{
	global $txt; // need $txt 'cause loadLanguage only fills in the setting's name
	loadLanguage('UAD');
	$config_vars = array_merge($config_vars, array(
		array(
			'select',
			'UAD_location',
			'name' => 'UAD_location',
			array(
				'0' => $txt['UAD_bottom_user_info'],
				'3' => $txt['UAD_top_user_info'],
				'2' => $txt['UAD_below_post'],
			),
		),
		'',
	));
}
Everything's working as it should now.