Installing extensions (libraries) as a local user

Are there provisions in php to use an installed extension from a local user? An example is that I want to install ming as a local user where I don't have access to the default extension directory or the system php.ini. If yes, how do I include (source) my local php. ini? I presume that I could put my extension_dir = "to my local extension dir". Is this possible or must I have write access to the php installed location to use 3rd party extensions? Thank you for any help!