Maybe I could just attach a small copper heat sink directly to a copper water block, similar to the ones on my motherboard and then point a heavyweight fan at it. I am not sure how to get a good connection though. I guess that solder is mostly silver so maybe that would be good enough? Probably there is special solder that is more conductive of heat, too.
I don't want to necessarily get a mega amount of heat dissipation from the heat sink, just enough to keep it from cooking out if the water pump seized up. That seems like something that is reasonably likely to be achievable.
Looking at the sizes involved the all in one water cooler is not that practical so I would just forget about that. I would have to have a 5 inch thick copper block which would weigh already 1000 grams or so without any heatsink!