@atrus
Please remember that what you are looking for is a "human" value, as opposed to the snapshot type of values the server can reliably provide. The reason why nginx does not provide what you are looking for may be that the server would have to provide several intervals to satisfy everyone (second, millisecond, minute, hour, etc.), and that is neither practical nor reliable. Such data could also be misleading, depending on your use case. From a server point of view, the best thing to do was to give a total number of requests served and let the admins do the math as they see fit.
However, the stub status module provides easy-to-read data that you can parse with a script in a loop, or such a script could dump the stats in a database and you could then read that. That is the best long-term solution to your problem. Please remember too that this database does not need to be SQL, it could be RRD-based for example, or just plain files, whatever suits you best.
Regards,