The kit to make these are found on InvisibleShoe.com. As a warning, you have to punch the hole between the toes yourself. I have a hole punch if any of my friends want to try though.
There are other methods (other hole punch configurations) other than this thong-sandal style, to play with.
As of tonight, these are getting a recommendation. I'll be field testing them for office work tomorrow.
Video is below.