php: number only hash?

In php is there a way to give a unique hash from a string, but that the hash was made up from numbers only?

example:

return md5(234); // returns 098f6bcd4621d373cade4e832627b4f6

but I need

return numhash(234); // returns 00978902923102372190 
(20 numbers only)

the problem here is that I want the hashing to be short.

edit: OK let me explain the back story here. I have a site that has a ID for every registered person, also I need a ID for the person to use and exchange (hence it can't be too long), so far the ID numbering has been 00001, 00002, 00003 etc...

1. this makes some people look more important
2. this reveals application info that I don't want to reveal.

To fix point 1 and 2 I need to "hide" the number while keeping it unique.

Edit + SOLUTION:

Numeric hash function based on the code by https://stackoverflow.com/a/23679870/175071

/**
 * Return a number only hash
 * https://stackoverflow.com/a/23679870/175071
 * @param $str
 * @param null $len
 * @return number
 */
public function numHash($str, $len=null)
{
    $binhash = md5($str, true);
    $numhash = unpack('N2', $binhash);
    $hash = $numhash[1] . $numhash[2];
    if($len && is_int($len)) {
        $hash = substr($hash, 0, $len);
    }
    return $hash;
}

// Usage
numHash(234, 20); // always returns 6814430791721596451