suPHP to FastCGI

I'm hoping someone can help or even offer some advice.

We've been using suPHP without problems (using a php.ini file with an include_path set). I wanted to change to FastCGI(PHP) to benefit from some performance boost.

All seemed to work apart from the php.ini file that we were using simply is not read.

I have also tried the following;

http://www.askapache.com/php/custom-phpini-tips-and-tricks.html

but now the PHP file wants to download instead of being parsed.

If anyone could offer any suggestions on how to use a custom php.ini file with FastCGI - would very much be appreciated.

M