Fingertip variations of pushing movements work the extensors in an isometric manner. They also help improve the mobility of the flexors. The forearm can become strained and overdeveloped from a lack of balanced training just the same as the shoulder, hips, lower legs. Basically muscle groups that are utilized in both push and pull movements should be trained in a balanced manner.
If you are not feeling your extensors being worked. You are probably not putting enough force upon them. Put your hands inside of shoulder width. If that doesnt challenge them, raise the intensity... You probably have fairly strong extensors. They counterbalance the flexors of course and you do utilize them even if you dont notice it... Also purchase some rubber bands to do isolated extensor training to improve their endurance.