<a href="#" id="liveagent_button_1"
   onclick="liveagent.startChatWithWindow('1', 'iframe');
   $('#someChat').attr('src', '%CHAT_LINK%')">
   Some button
</a>

<div class="iframe-wrap" style="position: fixed; bottom: 0; right: 0; height: 400px;">
    <iframe id="someChat" style="height: 100%;"></iframe>
</div>