You could specify a seperate FastCGI PHP daemon and add html to the extension setting. Use this new FastCGI server only for your .html PHP website.
FastCGIserver {
FastCGIid = PHP5
ConnectTo = <FastCGI binding>
Extension = php
}
FastCGIserver {
FastCGIid = PHP5_HTML
ConnectTo = <FastCGI binding>
Extension = php, html
}
Use the last FastCGI definition for the .html PHP website, and the first for all other PHP websites.
What kind of webapplication are you talking about btw? No offense, but it sounds like real bad webdesign if the .html extension is used for PHP.