You will have to use an iframe element that runs in the web context.
The source of the iframe would be another html file that would reference the remote script. Simple javascript functions are used to pass messages between the main body of your app and the iframe element.
I wrote a
blog post on this technique using the Customer Preview.
***Note, to update this for the Release Preview, take care to replace
ms-wwa --> ms-appx
and
ms-wwa-web --> ms-appx-web
in multiple places and multiple files. (In addition to other template changes.)