You can still select just those packages out of their repos. Obviously that can get tedious if there are a lot of them. But that’s pretty rare and at that point it’s worth asking, is that software really worth it? Is there a better installation method? Could it live in a cheoot/container?
But that’s not just in the Apt world, any system wide install would behave like that.
You need the mount point not the device. Probably something like
/media/Files