Just to confirm, you are benching over 500lbs?
Well, if that is your sticking point then you could try dead benches with the bar set on pins slightly below where the bar loses speed. Of course you could do them at chest level too. The point is that this will completely remove the stretch reflex and make the lift move much slower so you can't rely on momentum. The way that Josh Bryant advises to do them is for singles only. You want to start fairly light too. You could do something like 70%x1x8 the first week, then 75%x1x8 the next week, then 80%x1x6. Take a deload (or don't), then start back at 80%x1x6, 85%x1x4, and then work up to a near max the last week. Josh says you should be able to do about 90% on these from chest level. I did this and it definitely improved my speed off the chest as well as tightness (if you're not tight enough, the bar isn't moving off the pins) but now I'm getting stuck higher up. If you are going to do this with the pins higher up then you might want to increase the percentages.
Other than simply working on your sticking point and/or speed off the chest, the only thing that comes to mind is an exercise that Sheiko posted on his facebook page a while ago. A guy sent him a video of a special exercise to improve bar path where he was using bands but they were anchored somewhere by his feet (legs of the bench maybe?) so he would have to struggle a bit to maintain the correct bar path.