The cartridge pulls/pushes from the bottom of the tube only. The oil doesn't really circulate, it just sort of gets shook by road vibration. I suppose given a sufficient amount of ride time it would eventually blend completely. The "beat" oil in the cartridge will be of less viscosity. It would tend to be pulled though the orifices more easily. In more sophisticated "closed chamber" fork designs the oil doesn't circulate at all, the smaller volume of cartridge oil is held separately.I don't get why oil in a fork tube would not mix or circulate well. I'm not saying that what you've said isn't true, just that it doesn't make sense to me. Can you say more?
I thought of pumping the fork but it is pretty difficult to get much travel with the spring in place. I guess you could add some fresh oil and pump it, drain some more, and see if you can "exchange" the oil in the cartridge. The problem is that, I don't think you could bleed the cartridge properly without being able to stroke the damper rod fully. Mounting the fork back on the bike with air in the cartridge will certainly result in less than desired performance.bouncing up and down on the fork a few times helps evacuate a bit more oil.