Not so easy.
You can certainly make your own custom page with a progressbar (and a listview, etc.), and use a function to install the files (using File etc. just as you would inside a Section) - but it's a fair bit of hassle.
Simpler would be to create a custom UI altogether (similar to how ModernUI, ******odernUI, etc. are custom UIs) and customize the existing InstFiles type page.