Yep, I did look at the heated nozzles from a RRC a while ago but I don't think they'd fit a Disco (they're designed to mount on top of a bonnet rather than under the trailing edge). I wouldn't be surprised if LR re-used the parts but they were a bit expensive to buy and then have to mangle them to fit.
I was thinking in terms of aiming for the heater hoses rather than the rad ones, as the longer the pipe the more hassle it will be to cable tie it and stop it fouling anything. The heater being at the back of the engine bay will be closer to the existing washer hose runs, so all I'd need to do is disconnect the pump from the nozzles, take a new pipe from the pump, wrap it around the heater hose a few times and then reconnect to the nozzles.