Cineform should be an option - but I am hazy on the details because I don't use it.
If you are happy with image sequences, PNG has some lossless compression options that should prove satisfactory.
Also ... offline 2K editing in DNxHD with online conform to DPX may be more reasonable that you think. Its still a huge bandwidth hit on the system, but by the time you edit you should be able to have a lot less resources on your timeline and thus get better performance results. I don't know if that will be enough to tip your system into usable.
Just some scattershot ideas, maybe one will help.