Register new widget areas

First, register a new sidebar. The before_widget, after_widget, before_title and after_title arguments are optional and allow you to customize the HTML output.

genesis_register_sidebar(
	array(
		'name'=>'Custom Sidebar',
		'id' => 'sidebar-custom',
		'description' => 'This is a custom sidebar',
		'before_widget' => '<div id="%1$s" class="widget %2$s"><div class="widget-wrap">',
		'after_widget'  => "</div></div>",
		'before_title'  => '<h4 class="widgettitle">',
		'after_title'   => "</h4>"
	)
);

Then inject the sidebar into the appropriate hook with genesis_widget_area(). The function conditionally displays a widget area.

add_action( 'genesis_sidebar', 'child_do_sidebar' );
function child_do_sidebar() {
	genesis_widget_area( 'sidebar-custom',
		array(
			'before' => '<div id="sidebar-custom">',
		)
	);
}

See the available arguments for genesis_widget_area() in /genesis/lib/functions/widgetize.php

Update 28 Dec 2012: Replaced dynamic_sidebar() with genesis_widget_area()