Possible to pass a closure to usort in PHP?

Question

I have an array sorting function as follows:

public function sortAscending($accounts)
{
    function ascending($accountA, $accountB) {
        if ($accountA['AmountUntilNextTarget'] == $accountB['AmountUntilNextTarget']) {
            return 0;
        }
        return ($accountA['AmountUntilNextTarget'] < $accountB['AmountUntilNextTarget']) ? -1 : 1;
    }
    usort($accounts, $ascending);

    return $accounts;
}

Clearly this is not ideal as it is hard-coding the key to search for. I thought I would make this generic by passing the key as a param to outside function, however this is then out-of-scope in the inner function. I tried to get around this by using a closure, which would have access to the param, instead of an inner function as follows:

public function sortAscending($accounts, $key)
{
    $ascending = function($accountA, $accountB) {
        if ($accountsA[$key] == $accountB[$key]) {
            return 0;
        }
        return ($accountA[$key] < $accountB[$key]) ? -1 : 1;
    }
    usort($accounts, $ascending);

    return $accounts;
}

However usort() only accepts a function name, so this doesn't work. Can anyone see a (better?) way of achieving this?