OK, I have a working trivial plugin for this that just does a 30bit int for now. Seems to work ok - making a bag of 1000 values suggests it at least does a tolerable job. Though it does bother me a bit that in a whole load of tests I've not seen any number with less than a half-dozen digits. I'll let you numerics fanatics worry about that part.
So what sorts of values would be useful? Is just a 30bit int ok with any further cleverness being done in the image?
tim