Do you have access to the theme files? If so, try replacing <?php get_sidebar() ?>;
with this:
<?php
if( stristr($_SERVER['HTTP_USER_AGENT'],'android') === FALSE ) {
get_sidebar();
}
?>
Otherwise, what about access to the theme’s javascript file?
var ua = navigator.userAgent.toLowerCase();
var isAndroid = ua.indexOf("android") > -1;
if(isAndroid) {
// Do something!
// Perhaps target the CSS to hide the sidebar (display:none;)?
}
EDIT:
You can also try loading a stylesheet after the default one that targets mobile devices. Use the media attribute when loading the stylesheet:
<link href="https://wordpress.stackexchange.com/questions/31285/mobile.css" rel="stylesheet" type="text/css" media="only screen and (max-device-width: 480px)" />
Alternatively you can just add some declarations into your existing stylesheet:
// target small screens (mobile devices or small desktop windows)
@media only screen and (max-width: 480px) {
/* CSS goes here */
}