You can speculate on nonconvertible currencies with non-deliverable forwards. This is not offered by most retail brokerages.
Edit: yes, exactly
So where's the money making opportunity? You're short selling at the market (ie. non-official) rate, and have to buy back at the market rate. The only way you'll make money is if the market rate drops even more, but whether that happens is uncertain. This just sounds like run of the mill currency speculation.