This issue is best addressed in the Atheros forum.
In general though, dd-wrt (like most third-party firmware) only receives a binary blob from the OEM to support the wireless features, not actual source code. And if some feature either isn't implemented or configurable, there's nothing the router can do about it. IOW, the developers are at the mercy of the OEM in terms what is and isn't possible wrt wireless.
So as long as the feature is either already implemented by the OEM, or the OEM provides an API for configuration, you have a chance. But in some cases I know they do NOT (perhaps to give their own products an edge).