Sorry. But there is no automagic way to convert a static HTML site over to WordPress. Your customer should have told you upfront that he/she wanted a CMS.
You could install WordPress as a blog (domain.com/blog/WP/). The blog would be editable by your client in WordPress but the main site would be remain static HTML.
Another option is to reverse engineer your static HTML pages to work with another CMS product.
Cushy CMS might be all you need (watch their video to see how it works).
http://www.cushycms.com
Content Seed -
Available in ASP, PHP, or ASP.net
no database needed.
http://contentseed.com/
PowerCMS from Web Assist -
Requires PHP 5.2.3+
MySql database
http://www.webassist.com/dreamweaver-extensions/powercms-builder/
Best of luck,
Nancy O.
Alt-Web Design & Publishing
Web | Graphics | Print | Media Specialists
http://alt-web.com/
http://twitter.com/altweb