Instead of the javascript in each of your products, you can instead add the following to your product.tpl file (or anywhere else).
{if $err eq "options"}
<div class="ErrorMessage">{$lng.err_select_options}</div>
{/if}
Then add a language variable called "err_select_options"
This assumes you did add the additional select option described above and that you always want all options selected.
I'm working on an X-cart 4.1.11 site.