Magento – Prevent automatic URL rewrites created that include category URL key in product URL

Whenever I create a new product, Magento automatically creates unnecessary URL rewrites that include each category and subcategory combination, that use the categories' URL keys in the product path. For example, for a product product-name with the categories:

category
category > subcategory
category > subcategory > third

…Magento will automatically create URL rewrites with the following request paths:

/category/product-name
/category/subcategory/product-name
/category/subcategory/third/product-name

…as well as also creating the in-use URL rewrite with request path:

/product-name

My question is, even though I have the setting Use Categories Path for Product URLs set to No in:

System > Configuration > Catalog > Search Engine Optimizations

…how do I stop these additional URL rewrites from being created automatically?

Now, again, I realize that the site isn't linking to these additional paths anywhere on the site, but if for some reason a search engine picked up:

http://example.com/category/subcategory/third/product-name

…this would load! I'm nervous this will result in duplicate content being indexed by search engines. Since the Use Categories Path for Product URLs setting is set to No, and all links to the product on the site are pointing to:

http://example.com/product-name

…I want to stop Magento from creating these unnecessary URL rewrites automatically.

For reference, I tried truncating the core_url_rewrite table to zero (basically emptying it out) and reindexing the Catalog URL Rewrites in System > Index Management. This still results in Magento automatically creating these unnecessary URL rewrites.

Also, for reference, I am using Magento Community 1.9.1.

Please advise! Your help is much appreciated.