Try this: You want to put a dry cotton cloth or terrycloth towel on the bench under your shoulder blades (I use an old t-shirt). As the bar approaches the very tip of your ribs at the bottom of your ribcage think about squeezing your shoulder blades together as much as you can. The dry cloth should allow them to move freely even though you're under pressure from the bar. Pulling them together will give your pecs a nice full stretch, so even if you find you cannot get the bar to actually touch you can still get a good ROM. Make sense? Grip should be a bit wider than your shoulders. Imagine you are doing db flyes on the way up even though you are doing barbell presses. This activates the hell out of your pecs. Don't just press upward, scissor upward (its a mind thing). When all you do is just press straight up it does not activate as much of the pectoral. Know that your poundage will be far less, but you'll get a great pump.