Uploading a file

I have a web service for uploading a file. In PHP this service can be called like this:

$url = $base_url . '/api/import';

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, array(
    'file' => '@'.dirname(__FILE__).'/filename',
));
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type: multipart/form-data',
    'Authorization: Bearer ' . $access_token,
  ));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$output = curl_exec($ch);
curl_close($ch);

In Drupal I would like to use wsclient, since I am using it for the rest of the service calls. But I don't see how this can be done.

Is there any way to do this with wsclient, or I should just use drupal_http_request()?