14-2 wire on a 20amp circuit
Nope, you have to extend a 20A circuit with 12 AWG wire.  

The logic that "these will be lightly used receptacles" doesn't buy you a thing, because the safety of the wiring can't depend on how you use it. 

You are allowed to put NEMA 5-15 (common receptacles) on 20A circuits, due to a special exception. 

Even in the industrial parts of the Code, in the byzantine Tap Rules, such an extension would required a hardwired load of known value, or a single receptacle.  I'm sure you don't intend to install this: 



So if you're installing the common duplex 15A recep, what keeps you from plugging two 9A loads into it?