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.