From the PHP Manual section on Language Options:
Whether to enable the ability to force arguments to be passed by reference at function call time. This method is deprecated and is likely to be unsupported in future versions of PHP/Zend. The encouraged method of specifying which arguments should be passed by reference is in the function declaration. You’re encouraged to try and turn this option Off and make sure your scripts work properly with it in order to ensure they will work with future versions of the language (you will receive a warning each time you use this feature, and the argument will be passed by value instead of by reference). "[/quote]
If your application can use PHP4, you can simply set your domain to use PHP4 (from within the DreamHost control panel) and the Allow_call_time_pass_reference option will be set to “ON”.
That said, and to answer your actual question, there are two ways on DreamHost for you to edit php.ini to change certain lanuage options:
http://wiki.dreamhost.com/Installing_PHP5 / http://wiki.dreamhost.com/Installing_PHP4.
You should note that neither of these methods is supported by DreamHost Technical Support staff; if you go this route you are “on your own”.