You need to write naturally, as Google uses a natural language algorithm. What you are describing is called stemming
http://en.wikipedia.org/wiki/Stemming have a read of that, it will help you with your writing.
you MUST get away from writing for the search engines, and write for your clients, as that way, you will naturally use all the stemmed and symantically related words, which, overall will help your SEO a hell of a lot more.
BUT the simple answer is, you need to mix and match singlular and plural in the inbound anchor text.