Secret revealed: how can a bitcoin bank pay interest

I love this Q&A (as reported by CoinTelegraph here):

CoinTelegraph: Do you lend out the money that clients put on deposit with you — i.e., do you practice fractional reserve lending?
Josh Blatchford: Currently, no deposits are being lent out. Our trading platform,, operates with its own internal funds and the launch of Magnr does not change this. However, in the near future, a small proportion of client funds will be used for leveraged trades on our trading platform.
We have carefully modeled these risks and calculated a return that we can guarantee to our clients, ensuring a sustainable business model.

Where did I hear this before?