I built something similar years ago when I had a laptop with a really tiny hard drive. I would move a bunch of files to a cloud server, and left a bunch of files with no data on the hard drive. Then I wrote a file system filter driver which would watch for the files opening, catch the open request, and quickly download.

It was better than walking around with an external drive. But it was super slow. After I upgraded the laptop, I had no further use for it.