I wonder if anyone has mounted one chasis fan on the outside of the case where the other is mounted inside? Exhaust of the inner fan serving as the intake for the outer fan. How much would the volume of air being moved increase? There is no room for a slot fan nor a chasis fan inside the case.
There is always room for a fan or two roll a picture of your case up and We'll see what we can come up with for you, but Bump to hunter, no 'real' point in a pushpull on a case panel, but aesthetically it may work for you.