Shopping Cart Approach to time zones???

Is is possible update sitetimezone per session so when default site timezone updated per session/user ( both users and guests ) dates would display correct without hardcode? Can it be?
something like that?

function module_thisuser($create = TRUE) {
  global $user;
  if ($user->uid) {
    return $user->uid;
  }
  elseif (!isset($_SESSION['thisuser']) && $create) {
    $_SESSION['thisuser'] = md5(uniqid(rand(), TRUE));
 // some jquery grab user's timezone and
	simpleclock_timezone_update_site();// update default sitetime zone for user
  }
  return isset($_SESSION['thisuser']) ? $_SESSION['thisuser'] : FALSE;

 }