The URL Attribute needs to come from your Application entity, so will need to be calculated before you pass it in.
How does the JavaScript snippet work? Does it return a URL that you put into the iFrame, or does it does this itself?
If it returns a URL, you could return this value in a JavaScript action to a Nanoflow that you use as the datasource for the data view.
If the JavaScript just expects to inject into a specifically named iFrame, swap out the iFrame widget for an HTMLSnippet with the iFrame HTML in it before the JavaScript snippet.
Hope this helps