It's a little difficult to answer this question without knowing what website we are talking about, but my first question is:
Why weren't the other pages optimized?
It the time was taken to optimize one or two pages, why not go for broke and do all of them?
Here is what I would do.
- Go ahead and revisit the Supplemental Pages. Opitmize for the content on the page. Change the Title, Description and just for C's and G's, the meta keywords tags.
- Rearrage some of the content on the page. Redo the content if you can. Change a paragraph to bullet points, or ad a header <h1> title to the beginning of your content. Just make the pages fresh again.
- Create a brand new sitemap.xml file, and submit it to Google's Sitemaps.
- Add relative links from your homepage or one of the pages that show up in the SERPs. Reason? We know Google likes that page, and checks it out from time to time, and returns it for a SERP, so it's a relatively good page. A TEXT link from that page won't hurt.
Googlebot likes changes, it likes new content and it likes moving things about a bit. If your pages are refreshed, the algo will look at your pages in a new light. Might even pull them out of supplemental, but that's no guarantee.
Obviously, some IBL's from a neato source would be cool. If you can get a link to the page from a blog, or another site, well now I'm just being obvious.