Something like the code below works.
However, keep in mind that the app is any case served from the proxy, so your user will be waiting for the initial page load. Therefore using splash screens just for the sake of showing an extra screen may not provide a UX enhancement.
That being said, I could see splash screens be useful in cases where you want to initially load a very small payload and instruct the user to wait while the app is completely bootstrapped and displayed to user.
<body onload="mwl.timer('timer1', 2000, 1, 'mwl.switchClass(\'#splasher\',\'show\', \'hide\');mwl.switchClass(\'#content\',\'hide\', \'show\');')">
<div id="splasher" class="show">Splash</div>
<div id="content" class="hide">Content</div>