That would work, or you could just add the code to the top of the page:
<?php
$defaultAddress = "you@yourcompany.com";
if ($_POST['selection'] == "value 1") {
$defaultAddress = "sales@yourcompany.com";
} else if ($_POST['selection'] == "value 2") {
$defaultAddress = "sales@yourcompany.com";
}
?>
and then specify the email address as <?php echo($defaultAddress); ?> in universal email.