PHP: use a variable to reference a defined variable, w/o eval

PHP: use a variable to reference a defined variable, w/o eval

That title probably doesn't help much. I'm trying to figure out if there's
a way to get the value of a variable that has been set using define(...),
but using a 2nd variable to build the defined var's name. Example will be
clearer:
define('I_LOVE_YOU', 'xoxox');
$n = 'LOVE';
// how to get 'xoxox', using $n? This won't work:
$defd = 'I_'.$n.'_YOU';
echo $defd; // obviously echos 'I_LOVE_YOU', not 'xoxox'
// this will, but is awful
eval('echo I_'.$defd.'_YOU;'); // echos 'xoxox'
Is there any other way to do this, w/o resorting to eval?