You are correct, this is not currently an available feature, however there are plans for a coupon code module to be included in, at this stage CP v3.1 (Right now we're up to 3.0.2 with 3.0.3 soon to be released).. So it will still be some time yet, although I cannot give a specific date/time frame.
This topic has come up before though, so it's certainly something others have been working on to implement themselves..