Genesis child – dynamic header image

Hi,

I am trying to modify the contents of the widget area defined in the header (sidebar) of a Genesis child theme.

I have used the PHP Text Widget to use a simple PHP based ad image switch in the header widget from the header widget in the admin area:

<?php if ( is_home() ) { ?>
	...show ad 1
<?php }
else { ?>
	...show ad 2
<?php } ?>

however this seems cludgy and I want to place the decision logic in the functions.php instead of the widget in the admin area.

What is the most elegant way and best practice to achieve this?

Many thanks.