dips, decline bench, any motion that brings the elbows in and down like flexing your pecs for the ladies. I have a hard time working my lower pecs, as my lats want to take over the motion.
If you want to spend some time just to work them, do dips leaned forwards a touch. At the top of each rep really squeeze those pecs tight and lift your body as much as possible (without using lats). Focus on using the chest to lift your body instead of the tri's. Breath in twice per rep and you will get an extra stretch, just dont pass out.