WPMU Subsite to replace someone's existing website… redirects??

I am doing a new subsite for one of my clients. They have an existing (static HTML) website. Need to do 301 redirects for about 100 HTML pages to their corresponding new WP pages.

What I know so far is that I need to do 301 redirect, that these reside in the .htaccess file and the syntax is like this:

redirect 301 http://company-x.com/page1.html http://company-x/whatever-path/

Notice there is no automatic expression that can do the conversion from old to new path. Those redirects will need to be done line-by-line for all pages from the old website.

I see subsites do not have their own .htaccess. Would I need to put those hundred redirects in my main .htaccess? Is there a way to have a separate .htaccess for the subsite? Is there a better way?