Setting PHP Include Path on a per site basis?

Question

I can set the PHP include path in the php.ini:

include_path = /path/to/site/includes/

But then other websites are affected so

Answer 1

Erik Van Brakel gave, IMHO, one of the best answers.

More, if you're using Apache & Virtual hosts, you can set up includes directly in them. Using this method, you won't have to remember to leave php_admin commands in your .htaccess.