I had a similar problem once before. Following normal charcoal treatment, mix in Celite and filter the resultant celite/charcoal slurry through a (well packed) pad of Celite. Because the celite particles are larger, they disrupt the tight packing of the charcoal and reduce blockage. In my case, the celite retained most of the charcoal, and a 0.45 micron treatment removed the last traces.
I don't know what grade of charcoal I was using at the time, so there's no telling if it's going to help in your case, but probably worth a shot on test scale.