Maybe a peristalsis style pump to push the ice slush through?
Actually, given the temp of your coolant, I'm not sure flow matters all that much - who cares if the cpu/coolant delta is even 5C greater than it would have been with decent flow - just dial the coolant temp down that much more.
BTW, have you done any below-ambient cooling before? Just doing the "mad scientist" thing or do you actually expect to get usable additional speed over simply keeping the processor at ambient?