Styleswitcher or themeswitcher to allow user to switch back to standard view from mobile device

Wouldn’t it be enough to switch mobile/desktop via a $_SESSION variable, make the “switch to desktop link” include something like ?switchtodesktop=1 and have the header contain something like

session_start();
if ($_GET['switchtodesktop']) {
  $_SESSION['switchtodesktop'] = true;
}
$desktop = isset($_SESSION['switchtodesktop']);
[...]
if ($desktop) {
  // only desktop css without media queries
} else {
  // default stuff (media queries, like you have now ..)
}