try doing lying tri extensions with db, only keep your elbows at a 90 degree angle from the body, and bring the weight down to the other pec.
also, here's an exercise that i do. its kind of a hybrid between an extension, and a pressing movement. i was fuckin around one day, trying to think of something new. get on a bench like you are going to do some db presses. rotate your hands so that your palms are facing each other. as you do the extension, try to move them in a straight line, with your arms tight to the body (keep the palms facing each other the whole time.) this will require you to drop your elbows while doing the extension. the end of the db should touch your shoulders. the position that you are now in, should be very similiar to a CG bench press, only you hands are at your neck, and the palms are facing each other. now press and extend up at the same time, tryin to move the weight in a straight line back to the starting position. <--give these a try. let me know what you think. also, if my description doesn't make sense, let me know, and ill try to write it up better...