The other obvious choice is to configure your webserver to associate .html files with PHP. Basically what you normally do is associate .php or .phtml file extensions to run through the PHP engine. Just do what you did to configure that, only have it do so for .html files.
Please note this WILL incur a performance penalty as now ALL of your .html files will have to be parsed by the PHP engine, whereas normally only files ending with .php or whatever are redirected through the PHP engine before output.
But if your needs are simple enough, or you plan to put PHP code in many of your webpages, this may work for you. For larger sites with lots of typical HTML files (only text and graphics) and only a few pages with PHP code, this performance hit may not be acceptable. Your mileage may vary.