Protecting content for supporters only

I've seen this bounce around the forum but haven't found a solution to hide content and have it available for supporters only.

There is a great plugin that works with amember that does this, here it is:

http://wordpress.org/extend/plugins/hidepost/

It's perfect for what I'm trying to do, but the trick for me is to get it going for supporters only.

I copied some code from one of my other plugins thats been hacked and came up with this:

if ( function_exists(is_supporter) && !is_supporter() ) {
echo '<div class="wrap">';
echo '<div id="message" class="error"><p>This feature is limited to supporters only. Click here to find out how and why to become a supporter.</p></div>';
echo '<h2>'.__('Hidepost').'</h2>';
echo '</div>';
return;
}

Not sure if it's at the right place within the file or if its just completely wrong.

I attached a screenshot as the plugin has various restriction rules already setup for either role managers or admin, etc.

So how would I get this to work for supporters only?

Thanks,

George