I have a utility on my a1200 desktop tht can mount adfs as if it were the real disk. I used it to install games that were problematic with whdload and used the original installer with this app. Also for installing old diskmags like grapevine. It works perfectly, the only drawback is that disks that were no readable in workbench(some ndos disks from games) don't work.
I downloaded it fom aminet and among adf it could manage several disk formats, including the rare sinclair QL. I will look to see the name of the app and list it here, because already i don't remember its name.