How to implement mass redirects in Magento?

I am working on a large site migration where there are thousands of products that have had their URLs rewritten.

For reference, the original site had their products listed as /product, regardless of the category, subcategory, ec.

The same product on the new site is has its URL rewritten as /category/subcategory/product

Is there a way for me to implement a redirect on a large scale for all of the /product URLs that will eventually 404, so Google can have an easier time crawling everything after the migration?

submitted by /u/flowersinmyteeth
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