Passing variables outside of Codeigniter - SESSION doesn't work

I am running a Codeigniter 3.1.13 installation on a website where parts of the site are not running CI, just standard PHP not part of a framework.

I need to pass data from a script on the CI part to another script elsewhere on the same server (a couple of folders above CI). I thought I could just do it using the $_SESSION global, but the CI installation is using its own session storage (files in this instance) which the other script doesn't have access to with the $_SESSION global.

I guess there are a couple of questions:

1) Is there a way to have CI use the same PHP session storage as the rest of the server?
2) Or, is there another way to send the information out of CI to the other script (I don't want to use GET parameters in the request because I don't want them visible). For example, could CI "POST" the data to the other script?

Thanks in advance.