I tried this when I wanted a cold light head for my d5 but didn't have the funds to do so at the time( I finally got one from that well known auction site). Go to a plastic supply store and purchase a piece of translucent acrylic I tried a piece of 1/4" but an 1/8th would be better as it wouldn't absorb as much light. Get them to cut it just slightly larger than the condensors. Then when you get it home trace around the housing (condensor) and remove the circle of protective paper and remove the paper on the otherside then place this under the condensor and above the neg carrier. You may have to use electrical tape to mask off some of the stray light.
Try making a print with the plastic in place.the light from the condensors will be even above the plastic which will then be diffused before it passes through the neg. if it works and print times aren't to long you can cut the plastic to fit permanently under the condensors. The price of the acrylic shold only be a couple of bucks.