The curl function in WebDriverBase.php has this code:

foreach ($extra_opts as $option => $value) {
  curl_setopt($curl, $option, $value);
}

It would be nice to be able to pass $extra_opts to this function for one curl invocation but I don't see how to do this. Put another way, if I'm sending a message to selenium by making a call like:

$session->open("http://www.foo.com");

I don't see how to add extra curl options for that call.

Perhaps adding an additional argument named $extra_opts to __call in WebDriverBase.php would do it at least for the "simple" messages but I bet there are a number of ways. I'll take a crack at a patch if you're interested.