How to allow mixed case characters in multisite site name?

generally speaking this is a big hack

we have a

add_filter("wpmu_validate_blog_signup", "my_validate");

and from here on you have to bypass the exact error.
I can not show you my exact code because of some copyright issues, but at least a part of it. In this example we add hyphens to the allowed characters. I also solved it thru google and stack overflow

function my_validate($result)
{
$errors = $result['errors'];


// we only want to filter if there is an error

if (!is_object($errors))
{
    return $result;
}

// create a new var to hold errors

$newerrors = new WP_Error();


// loop through the errors and look for the one we are concerned with

foreach($errors->errors as $key => $value)
{

    // if the error is with the blog name, check to see which one

    if ($key == 'blogname')
    {
        foreach($value as $subkey => $subvalue)
        {
            switch ($subvalue)
            {
            case 'Site names can only contain lowercase letters (a-z) and numbers.':
                $allowedchars="-";

                // so whatever you do, you can add something to the allowedchars and bypass the preg match.
// by the way , the exact error case you need to get from the language file
                $allowed = '/[a-z0-9' . $allowedchars . ']+/';
                preg_match($allowed, $result['blogname'], $maybe);
                if ($result['blogname'] != $maybe[0])
                {

                    // still fails, so add an error to the object

                    $newerrors->add('blogname', __("Only lowercase letters and numbers allowed"));
                }

                continue;