Array_Map using multiple native callbacks?

Yes, just pass the result of one mapping into another:

$result = array_map(
    'mysql_real_escape_string',
    array_map(
        'trim',
        array_map(
            'strtoupper',
            $your_array
        )
    )
);

You can also use a callback in PHP 5.3+:

$result = array_map(function($x){
    return mysql_real_escape_string(trim(strtoupper($x)));
}, $your_array);

or earlier (in versions of PHP lower than 5.3):

$result = array_map(
    create_function('$x','return mysql_real_escape_string(trim(strtoupper($x)));'),
    $your_array
);

You'll have to do it like this:

$exclude = array_map(function($item) {
    return mysql_real_escape_string(strtoupper(trim($item)));
}, explode("\n", variable_get('gs_stats_filter', 'googlebot')));

You could also do something like:

  $exclude = array_map(function($item) {
     return trim(strtoupper(mysql_real_escape_string($item)));
  }, explode(...));

or something. Pass in an anonymous function that does all that stuff.

Hope that helps.

Good luck :)