Hi,
You could add one or several rules to your robots.txt to disallow the menu item you don't want to be indexed.
You could also set the "force canonical URLs on listings" to "use canonical URL and generate it if missing" in the HikaShop configuration.
In that case, just tell your client to browse for the product page on the frontend after creating a product. The system will then auto fill the canonical URL with the correct link. In fact, he doesn't even have to go to the product page, just the listing where that product page is listed with the correct URL.