Let's say you wanted to encode a single decimal digit using this PI method. So, to start, you list out PI until you get all the possible decimal digits:
03 14159 26535 897
01 23456 78901 234
There, that's all of them. I cheated a bit and put a zero in the front, as the first zero in the expansion is another 10 digits or so away. So now, we can represent any decimal digit by indexing into PI!
Now, extrapolate this out to every possible 100GB file, and the binary representation of PI.