My other thought is to reverse the rear fan and have this too blow inwards,
You have the germ of a good idea. The problem is that most fans don't respond well to fighting each other like you propose. By the way, the force of warmer rising air is very weak and will be irrelevant in your situation.
Before irretrievably chopping up your case, try this.
Get two of the higher speed Scythe Gentle Typhoon fans plus a fan speed controller. This one is good fan controller because it will always generate reproducible speeds, and it has a lot of speeds to select from:http://www.performance-pcs.com/catalog/ ... s_id=25981
Here is the experiment that I think will work. Block off the rear fan and the rear vents. Try just a single 120mm GT fan on the front. This will likely bring in more air than two fans fighting each other, and all the air will be forced out through your PSU. Keep in mind that the size of the case and the number of fans are not relevant. What is relevant is the amount of air flowing through the case and the amount of heat that air is able to carry away with it. Everything else is just a means to this end.
If there are two fans that can tolerate fighting each other with both pushing air in, it will be the Scythe Gentle Typhoon fans. The one area which they are the best in, is performing under high static pressure.
If you have the ability to mount two 92mm fans on the front, I would try this with two 92mm GTs. That might work even better than a single 120mm.... and will give you some redundancy in the event of a fan failure.