After browsing for a few minutes for ways of making deleted files totally unrecoverable, I had an idea which I haven't tried yet, but it seems like it should work.

Open a notepad file and type Om mane padme hum and copy paste ten times or so, then select all and repeat the copy paste process ten more times or so... and keep repeting this till you have lots and lots of "Om mane padme hum"s

save it and create a new folder to put it in
select the file and copy paste, paste, paste, paste, paste........................................
you get the idea

Once the folder is sufficiently large, copy paste the folder in another folder untill you have maxed out your disk space

finally delete everything you just did, and voila, the free space on your disk now has leftovers that is nothing but "Om mane padme hum"s

As I said, I haven't tried this yet.