How to use function’s default parameter in PHP

I want to do something like this.

function add($num1, $num2 = 1) {
    return $num1 + $num2;
}

$bool = true; // Can be true or false

if($bool) {
    add(5, 5);
} else {
    add(5);
}

I was asking me, if it is possible to write this logic in one line like, without repeating the default value:

add(5, $bool ? 5 : USE_DEFAULT_PARAMETER);